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Black Holes

Introduction to Black Holes

Black holes are objects so dense that not even light can escape their gravity, and since nothing can travelfaster than light, nothing can escape from inside a black hole. On the other hand, a black hole exerts thesame force on something far away from it as any other object of the same mass would. For example, if ourSun was magically crushed until it was about 1 mile in size, it would become a black hole, but the Earthwould remain in its same orbit.

Even back in Isaac Newton's time, scientists speculated that such objects could exist, even though we nowknow they are more accurately described using Einstein's General Theory of Relativity. Using this theory,black holes are fascinating objects where space and time become so warped that time practically stops inthe vicinity of a black hole.

Contrary to popular belief, there is a great deal of observational evidence for the existence of two types ofblack holes; those with masses of a typical star, and those with masses of a typical galaxy.

The former type have measured masses ranging from 4 to 15 Suns, and are believed to be formed duringsupernova explosions. The after-effects are observed in some X-ray binaries known as black holecandidates.

On the other hand, galaxy-mass black holes are found in Active Galactic Nuclei (AGN). These are thoughtto have the mass of about 10 to 100 billion Suns. The mass of one of these supermassive black holes hasrecently been measured using radio astronomy. X-ray observations of iron in the accretion disks mayactually be showing the effects of such a massive black hole as well.

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Journey into a Black HoleSee an animation of the suspected black hole at the heart of the galaxy M87. You will need the appropriatesoftware and drivers to view it.

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[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ]

AaccretionAccumulation of dust and gas into larger bodies such as stars, planets and moons.

accretion diskA relatively flat sheet of gas and dust surrounding a newborn star, a black hole, or any massive objectgrowing in size by attracting material.

active galactic nuclei (AGN)It is believed that these are normal galaxies with a massive black hole accreting gas at its center, thusproducing enormous amounts of energy at all wavelengths of the electromagnetic spectrum.

Tell me about AGN!

Tell me more about AGN!

angstromA unit of length equal to 0.00000001 centimeters. Scientists sometimes write this as 1 x 10-8 cm (seescientific notation).

angular momentumA quantity obtained by multiplying the mass of an orbiting body by its velocity and the radius of its orbit.According to the conservation laws of physics, the angular momentum of any orbiting body must remainconstant at all points in the orbit, i.e., it cannot be created or destroyed. If the orbit is elliptical the radiuswill vary. Since the mass is constant, the velocity changes. Thus planets in elliptical orbits travel faster atperiastron and more slowly at apastron. A spinning body also possesses spin angular momentum.

apoapsisThe point in an orbit when the two objects are farthest apart. Special names are given to this orbital pointfor commonly used systems. For example, the point of greatest separation of two stars, as in a binary starorbit, is called apastron; the point in its orbit where a planet is farthest from the Sun is called aphelion; thepoint in its orbit where an Earth satellite is farthest from the Earth is called apogee.

Ariel V

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A UK X-ray mission, also known as UK-5

Tell me more about Ariel V

ASCAThe Japanese Asuka spacecraft (formerly Astro-D)

Tell me more about ASCA

ASMAll Sky Monitor. Many high-energy satellites have carried ASM detectors, including the ASM on Vela5B, Ariel V, and the Rossi X-ray Timing Explorer.

Astro EA new X-ray/gamma-ray mission being built jointly by the United States and Japan. Astro E currently hasan estimated launch date of the year 2000.

Tell me more about Astro E

astronomical unit (AU)149,597,870 km; the average distance from the Earth to the Sun.

astronomyThe scientific study of matter in outer space, especially the positions, dimensions, distribution, motion,composition, energy, and evolution of celestial bodies and phenomena.

astrophysicsThe part of astronomy that deals principally with the physics of stars, stellar systems, and interstellarmaterial.

atmosphereThe gas that surrounds a planet or star. The Earth's atmosphere is made up of mostly nitrogen, while theSun's atmosphere consists of mostly hydrogen.

AXAFThe Advanced X-ray Astrophysics Facility. AXAF is currently scheduled to be launched by the SpaceShuttle in August, 1998.

Tell me more about AXAF

BBalmer lines (J. Balmer)Emission or absorption lines in the spectrum of hydrogen that arise from transitions between the second(or first excited) state and higher energy states of the hydrogen atom.

BBXRTBroad Band X-Ray Telescope on Astro-1 shuttle flight (Dec. 1990)

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binary starsBinary stars are two stars that orbit around a common center of mass. An X-ray binary is a special casewhere one of the stars is a collapsed object such as a white dwarf, neutron star, or black hole. Matter isstripped from the normal star and falls onto the collapsed star, producing X-rays.

Tell me about X-ray binary stars

Tell me more about X-ray binary stars

black holeAn object whose gravity is so strong that not even light can escape from it.

Tell me about X-rays from black holes

Tell me about gamma-rays from black holes and neutron stars

Tell me more about black holes

black-hole dynamic laws; laws of black-hole dynamicsFirst law of black hole dynamics:For interactions between black holes and normal matter, the conservation laws of mass-energy,electric charge, linear momentum, and angular momentum, hold. This is analogous to the first lawof thermodynamics.

1.

Second law of black hole dynamics:With black-hole interactions, or interactions between black holes and normal matter, the sum of thesurface areas of all black holes involved can never decrease. This is analogous to the second law ofthermodynamics, with the surface areas of the black holes being a measure of the entropy of thesystem.

2.

blackbody radiationThe radiation -- the radiance at particular frequencies all across the spectrum -- produced by a blackbody --that is, a perfect radiator (and absorber) of heat. Physicists had difficulty explaining it until Planckintroduced his quantum of action.

blackbody temperatureThe temperature of an object if it is re-radiating all the thermal energy that has been added to it; if anobject is not a blackbody radiator, it will not re-radiate all the excess heat and the leftover will go towardincreasing its temperature.

blueshiftAn apparent shift toward shorter wavelengths of spectral lines in the radiation emitted by an object causedby the emitting object moving toward the observer. See also Doppler effect.

Boltzmann constant; k (L. Boltzmann)A constant which describes the relationship between temperature and kinetic energy for molecules in anideal gas. It is equal to 1.380622 x 10-23 J/K (see scientific notation).

Brahe, Tycho 1546 - 1601(a.k.a Tyge Ottesen) Danish astronomer whose accurate astronomical observations formed the basis forJohannes Kepler's laws of planetary motion. (132 k GIF)



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bremsstrahlung"braking radiation", the main way very fast charged particles lose energy when traveling through matter.Radiation is emitted when charged particles are accelerated. In this case, the acceleration is caused by theelectromagnetic fields of the atomic nuclei of the medium.

CcalibrationA process for translating the signals produced by a measuring instrument (such as a telescope) intosomething that is scientifically useful. This procedure removes most of the errors caused by environmentaland instrumental instabilities.

CGROThe Compton Gamma Ray Observatory

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Chandrasekhar limit (S. Chandrasekhar; 1910 - 1995)A limit which mandates that no white dwarf (a collapsed, degenerate star) can be more massive than about1.4 solar masses. Any degenerate object more massive must inevitably collapse into a neutron star.

cluster of galaxiesA system of galaxies containing from a few to a few thousand member galaxies which are allgravitationally bound to each other.

collecting areaThe amount of area a telescope has that is capable of collecting electromagnetic radiation. Collecting areais important for a telescope's sensitivity: the more radiation it can collect (that is, the larger its collectingarea), the more sensitive it is to dim objects.

Compton effect (A.H. Compton; 1923)An effect that demonstrates that photons (the quantum of electromagnetic radiation) have momentum. Aphoton fired at a stationary particle, such as an electron, will impart momentum to the electron and, sinceits energy has been decreased, will experience a corresponding decrease in frequency.

Tell me how gamma-ray astronomers use the Compton effect

CopernicusNASA ultraviolet/X-ray mission, also known as OAO-3

Tell me more about Copernicus

Copernicus, Nicolaus 1473 - 1543Polish astronomer who advanced the heliocentric theory that the Earth and other planets revolve aroundthe Sun. This was highly controversial at the time as the Ptolemaic view of the universe, which was theprevailing theory for over 1000 years, was deeply ingrained in the prevailing philosophy and religion. (Itshould be noted, however, that the heliocentric idea was first put forth by Aristarcus of Samos in the 3rdcentury B.C., a fact known to Copernicus but long ignored.) (125 k GIF).

corona (plural: coronae)



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The uppermost level of the solar atmosphere, characterized by low densities and high temperatures (>1,000,000 degrees K).

Tell me about X-rays from the Sun's corona

Tell me about X-rays from other stellar coronae

COS-BA satellite launched in August 1975 to study extraterrestrial sources of gamma-ray emission.

Tell me more about COS-B

cosmic background radiation; primal glowThe background of radiation mostly in the frequency range 3 x 108 to 3 x 1011 Hz (see scientific notation)discovered in space in 1965. It is believed to be the cosmologically redshifted radiation released by the BigBang itself.

cosmic raysAtomic nuclei (mostly protons) and electrons that are observed to strike the Earth's atmosphere withexceedingly high energies.

cosmological constant; LambdaThe constant introduced to the Einstein field equation, intended to admit static cosmological solutions. Atthe time the current philosophical view was the steady-state model of the Universe, where the Universehas been around for infinite time. Early analysis of the field equation indicated that general relativityallowed dynamic cosmological models only (ones that are either contracting or expanding), but no staticmodels. Einstein introduced the most natural aberration to the field equation that he could think of: theaddition of a term proportional to the spacetime metric tensor, g, with the constant of proportionality beingthe cosmological constant:

G + Lambda g = 8 pi T.

Hubble's later discovery of the expansion of the Universe indicated that the introduction of thecosmological constant was unnecessary; had Einstein believed what his field equation was telling him, hecould have claimed the expansion of the Universe as perhaps the greatest and most convincing predictionof general relativity; he called this the "greatest blunder of my life."

cosmological distanceA distance far beyond the boundaries of our Galaxy. When viewing objects at cosmological distances, thecurved nature of spacetime could become apparent. Possible cosmological effects include time dilationand redshift.

cosmological redshiftAn effect where light emitted from a distant source appears redshifted because of the expansion ofspacetime itself. Compare Doppler effect.

cosmologyThe astrophysical study of the history, structure, and constituent dynamics of the universe.



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Dde Broglie wavelength (L. de Broglie; 1924)According to quantum mechanics all particles also have wave characteristics, where the wavelength of aparticle is inversely proportional to its momentum and the constant of proportionality is the Planckconstant.

DeclinationA coordinate which, along with Right Ascension, may be used to locate any position in the sky.Declination is analogous to latitude for locating positions on the Earth.

deconvolutionAn image processing technique that removes features in an image that are caused by the telescope itselfrather than from actual light coming from the sky.

densityThe amount of mass of any substance which can be contained in one cubic centimeter. Measured in gramsper cubic centimeter (or kilograms per liter); the density of water is 1.0; iron is 7.9; lead is 11.3.

disk (of planet or other object)The apparent circular shape that the Sun, a planet, or a moon displays when seen in the sky or through atelescope.

Doppler effect (C.J. Doppler)The apparent change in wavelength of sound or light caused by the motion of the source, observer or both.Waves emitted by a moving object as received by an observer will be blueshifted (compressed) ifapproaching, redshifted (elongated) if receding. It occurs both in sound and light. How much thefrequency changes depends on how fast the object is moving toward or away from the receiver. Comparecosmological redshift.

EeccentricNon-circular; elliptical (applied to an orbit).

eccentricityA value that defines the shape of an ellipse or planetary orbit. The eccentricity of an ellipse (planetaryorbit) is the ratio of the distance between the foci and the major axis. Equivalently the eccentricity is(ra-rp)/(ra+rp) where ra is the apoapsis distance and rp is the periapsis distance.

eclipseThe cutting off, or blocking, of light from one celestial body by another.

eclipticThe plane of Earth's orbit about the Sun

Eddington limit (Sir A. Eddington)The theoretical limit at which the photon pressure would exceed the gravitational attraction of a



light-emitting body. That is, a body emitting radiation at greater than the Eddington limit would break upfrom its own photon pressure.

Einstein, Albert 1879 - 1955German-American physicist; developed the Special and General Theories of Relativity which along withQuantum Mechanics is the foundation of modern physics. (32 k GIF)

ejectaMaterial that is ejected. Used mostly to describe the content of a massive star that is propelled outward in asupernova explosion.

electromagnetic spectrumThe full range of frequencies, from radio waves to gamma-rays, that characterizes light.

Introduce me to the electromagnetic spectrum

Tell me more about the electromagnetic spectrum

electromagnetic waves (radiation)Another term for light. Light waves are fluctuations of electric and magnetic fields in space.

electronA particle commonly found in the outer layers of atoms with a negative charge. The electron has only0.0005 the mass of the proton.

electron voltThe change of potential energy experienced by an electron moving from a place where the potential has avalue of V to a place where it has a value of (V+1 volt). This is a convenient energy unit when dealingwith the motions of electrons and ions in electric fields; the unit is also the one used to describe the energyof X-rays and gamma-rays. A keV (or kiloelectron volt) is equal to 1000 electron volts. An MeV is equalto one million electron volts. A GeV is equal to one billion (109) electron volts. A TeV is equal to amillion million (1012) electron volts.

elementsThe fundamental kinds of atoms that make up the building blocks of matter, which are each shown on theperiodic table of the elements. The most abundant elements in the universe are hydrogen and helium.These two elements make up about 80and 20 % of all the matter in the universe respectively. Despitecomprising only a very small fraction the universe, the remaining heavy elements can greatly influenceastronomical phenomena. About 2 % of the Milky Way's disk is comprised of heavy elements.

ellipseOval. That the orbits of the planets are ellipses, not circles, was first discovered by Johannes Kepler basedon the careful observations by Tycho Brahe.

erg/secA form of the metric unit for power. It is equal to 10-10 kilowatts (see scientific notation).

event horizonThe radius that a spherical mass must be compressed to in order to transform it into a black hole, or theradius at which time and space switch responsibilities. Once inside the event horizon, it is fundamentally



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impossible to escape to the outside. Furthermore, nothing can prevent a particle from hitting the singularityin a very short amount of proper time once it has entered the horizon. In this sense, the event horizon is a"point of no return". See Schwarzschild radius.

evolved starA star near the end of its lifetime when most of its fuel has been used up. This period of the star's life ischaracterized by loss of mass from its surface in the form of a stellar wind.

EXOSATEuropean Space Agency's X-ray Observatory

Tell me more about EXOSAT

extragalacticOutside of, or beyond, our own galaxy.

FFast Fourier Transformation (FFT)A Fourier Transform is the mathematical operation that takes measurements made with a radiointerferometer and transforms them into an image of the radio sky. The Fast Fourier Transform istechnique used by computer programs that allows the Fourier Transform to be computed very quickly.

Fermi accelerationIn order to explain the origins of cosmic rays, Enrico Fermi (1949) introduced a mechanism of particleacceleration, whereby charged particles bounce off moving interstellar magnetic fields and either gain orlose energy, depending on whether the "magnetic mirror" is approaching or receding. In a typicalenvironment, he argued, the probability of a head-on collision is greater than a head-tail collision, soparticles would be accelerated on average. This random process is now called 2nd order Fermiacceleration, because the mean energy gain per "bounce" is dependent on the "mirror" velocity squared.Bell (1978) and Blandford and Ostriker (1978) independently showed that Fermi acceleration bysupernova remnant (SNR) shocks is particularly efficient, because the motions are not random. A chargedparticle ahead of the shock front can pass through the shock and then be scattered by magneticinhomogeneities behind the shock. The particle gains energy from this "bounce" and flies back across theshock, where it can be scattered by magnetic inhomogeneities ahead of the shock. This enables the particleto bounce back and forth again and again, gaining energy each time. This process is now called 1st orderFermi acceleration, because the mean energy gain is dependent on the shock velocity only to the firstpower.

frequencyA property of a wave that describes how many wave patterns or cycles pass by in a period of time.Frequency is often measured in Hertz (Hz), where a wave with a frequency of 1 Hz will pass by at 1 cycleper second.

FTOOLSA suite of software tools developed at the OGIP for general and mission-specific manipulation of FITSfiles.

FTP



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File Transfer Protocol -- A widely available method for transferring files over the Internet.

Ggalactic haloA spherical region surrounding the center of a galaxy. This region may extend beyond the luminousboundaries of the galaxy and contain a significant fraction of the galaxy's mass. Compared to cosmologicaldistances, objects in the halo of our galaxy would be very nearby.

galaxyA component of our universe made up of gas and a large number (usually more than a million) of starsheld together by gravity.

Galilei, Galileo (1564 - 1642)An Italian scientist, Galileo was renowned for his epoch making contribution to physics, astronomy, andscientific philosophy. He is regarded as the chief founder of modern science. He developed the telescope,with which he found craters on the Moon and discovered the largest moons of Jupiter. Galileo wascondemned by the Catholic Church for his view of the cosmos based on the theory of Copernicus. (14 kGIF)

gamma-rayThe highest energy, shortest wavelength electromagnetic radiations. Usually, they are thought of as anyphotons having energies greater than about 100 keV.

gravitational collapseWhen a massive body collapses under its own weight. (For example, interstellar clouds collapse to becomestars until the onset of nuclear fusion stops the collapse.)

Gamma Ray Imaging Platform (GRIP)A balloon-borne gamma-ray telescope made by a group at the California Institute of Technology. It hashad many successful flights.

Gamma-Ray Imaging Spectrometer (GRIS)

Gamma-Ray Burst (GRB)Plural is GRBs. A burst of gamma-rays from space lasting from a fraction of a second to many minutes.There is no clear scientific consensus as to their cause or even their distance.

Tell me about Gamma-Ray Bursts

Tell me more about Gamma-Ray Bursts

general relativityThe geometric theory of gravitation developed by Albert Einstein, incorporating and extending the theoryof special relativity to accelerated frames of reference and introducing the principle that gravitational andinertial forces are equivalent.

Giant Molecular Cloud (GMC)Massive clouds of gas in interstellar space composed primarily of hydrogen molecules (two hydrogen



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atoms bound together), though also containing other molecules observable by radio telescopes. Theseclouds can contain enough mass to make several million stars like our Sun and are often the sites of starformation.

GingaThe third Japanese X-ray mission, also known as Astro-C.

Tell me more about Ginga

gravitational radiusSee event horizon.

gravityA mutual physical force attracting two bodies.

GSFCGoddard Space Flight Center

guest starThe ancient Chinese term for a star that newly appears in the night sky, and then later disappears. Later,the Europeans called this a nova.

HHawking radiation (S.W. Hawking; 1973)The theory that black holes emit radiation like any other hot body. Virtual particle-antiparticle pairs areconstantly being created in supposedly empty space. Occasionally, a pair will be created just outside theevent horizon of a black hole. There are three possibilities:

both particles are captured by the hole;1.

both particles escape the hole;2.

one particle escapes while the other is captured.3.

The first two cases are straightforward; the virtual particle-antiparticle pair recombine and return theirenergy back to the void via the uncertainty principle.It is the third case that interests us. In this case, one of the particles has escaped (and is speeding away toinfinity), while the other has been captured by the hole. The escapee becomes real and can now bedetected by distant observers. But the captured particle is still virtual; because of this, it has to restoreconservation of energy by assigning itself a negative mass-energy. Since the hole has absorbed it, the holeloses mass and thus appears to shrink. From a distance, it appears as if the hole has emitted a particle andreduced in mass.The rate of power emission is proportional to the inverse square of the hole's mass; thus, the smaller a holegets, the faster and faster it emits Hawking radiation. This leads to a runaway process; what happens whenthe hole gets very small is unclear; quantum theory seems to indicate that some kind of "remnant" mightbe left behind after the hole has emitted away all its mass-energy.

Hawking temperatureThe temperature of a black hole caused by the emission of Hawking radiation.



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HEAOThe High Energy Astrophysical Observatory satellite series

Tell me more about HEAO-1

Tell me more about HEAO-2 (Einstein Observatory)

Tell me more about HEAO-3

HEASARCHigh Energy Astrophysics Science Archive Research Center

Herschel, Sir William (1738 - 1822)Sir William Herschel was a renowned astronomer who first detected the infrared region of theelectromagnetic spectrum in 1800.

Hertz, Heinrich (1857 - 1894)A German physics professor who did the first experiments with generating and receiving electromagneticwaves, in particular radio waves. In his honor, the units associated with measuring the cycles per second ofthe waves (or the number of times the tip-tops of the waves pass a fixed point in space in 1 second of time)is called the hertz.

hertz; Hz (after H. Hertz, 1857 - 1894)The derived SI unit of frequency, defined as a frequency of 1 cycle per second.

HSTHubble Space Telescope

Hubble, Edwin P. 1889 - 1953American astronomer whose observations proved that galaxies are "island universes", not nebulae insideour own galaxy. His greatest discovery was the linear relationship between a galaxy's distance and thespeed with which it is moving. The Hubble Space Telescope is named in his honor. (58 k GIF)

Hubble constant; Ho (E.P. Hubble; 1925)The constant which determines the relationship between the distance to a galaxy and its velocity ofrecession due to the expansion of the Universe. Since the Universe is self-gravitating, it is not trulyconstant. In cosmology, it is defined as

H = (da/dt)/a,

where a is the 4-radius of the Universe. When evaluated for the present, it is written H0 = Hnow.The Hubble constant is not known to great accuracy (only within about a factor of 2), but is believed to liesomewhere between 50 and 100 km/s/Mpc.

Hubble's law (E.P. Hubble; 1925)A relationship discovered between distance and radial velocity. The further away a galaxy is from us, thefaster it is receding from us. The constant of proportionality is the Hubble constant, H_0. The cause isinterpreted as the expansion of spacetime itself.

Huygens, Christiaan (1629 - 1695)A Dutch physicist who was the leading proponent of the wave theory of light. He also made important



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contributions to mechanics, stating that in a collision between bodies, neither loses nor gains ``motion''(his term for momentum). In astronomy, he discovered Titan (Saturn's largest moon) and was the first tocorrectly identify the observed elongation of Saturn as the presence of Saturn's rings. (88 k GIF)

IIKISpace Research Institute (Russia)

implosionA violent inward collapse. An inward explosion.

infraredElectromagnetic radiation at wavelengths longer than the red end of visible light and shorter thanmicrowaves (roughly between 1 and 100 microns). Almost none of the infrared portion of theelectromagnetic spectrum can reach the surface of the Earth, although some portions can be observed byhigh-altitude aircraft (such as the Kuiper Observatory) or telescopes on high mountaintops (such as thepeak of Mauna Loa in Hawaii).

inclinationThe inclination of a planet's orbit is the angle between the plane of its orbit and the ecliptic; the inclinationof a moon's orbit is the angle between the plane of its orbit and the plane of its primary's equator.

imageIn astronomy, a picture of the sky.

Tell me about how astronomers use images

interstellar mediumThe gas and dust between stars, which fills the plane of the Galaxy much like air fills the world we live in.For centuries, scientists believed that the space between the stars was empty. It wasn't until the eighteenthcentury, when William Herschel observed nebulous patches of sky through his telescope, that seriousconsideration was given to the notion that interstellar space was something to study. It was only in the lastcentury that observations of interstellar material suggested that it was not even uniformly distributedthrough space, but that it had a unique structure.

ionsAn atom with one or more electrons stripped off, giving it a net positive charge.

ionic (or ionized) gasGas whose atoms have lost or gained electrons, causing them to be electrically charged. In astronomy, thisterm is most often used to describe the gas around hot stars where the high temperature causes atoms tolose electrons.

IUEInternational Ultraviolet Explorer



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JjetsBeams of particles, usually coming from an active galactic nucleus or a pulsar. Unlike a jet airplane, whenthe stream of gas is in one direction, astrophysical jets come in pairs with each jet aiming in oppositedirections.

Kkelvin (after Lord Kelvin, 1824 - 1907)A temperature scale often used in sciences such as astronomy. The fundamental SI unit of thermodynamictemperature defined as 1/273.16 of the thermodynamic temperature of the triple point of water. The Kelvintemperature scale is just like the Celsius scale except that the freezing point of water, zero degrees Celsius,is equal to 273 degrees Kelvin. [ K = C + 273o => F = 9/5C + 32o]

Kepler, Johannes 1571 - 1630German astronomer and mathematician. Considered a founder of modern astronomy, he formulated thefamous three laws of planetary motion. They comprise a quantitative formulation of Copernicus's theorythat the planets revolve around the Sun. (71 k GIF)

Kepler's laws (J. Kepler)Kepler's first lawA planet orbits the Sun in an ellipse with the Sun at one focus.

Kepler's second lawA ray directed from the Sun to a planet sweeps out equal areas in equal times.

Kepler's third lawThe square of the period of a planet's orbit is proportional to the cube of that planet's semimajor axis; theconstant of proportionality is the same for all planets.

kilogram (kg)One kilogram is equivalent to 1,000 grams or 2.2 pounds; the mass of a liter of water. The fundamental SIunit of mass, it is the only SI unit still maintained by a physical artifact: a platinum-iridium bar kept in theInternational Bureau of Weights and Measures at Sevres, France.

kinematicsRefers to the calculation or description of the underlying mechanics of motion of an astronomical object.For example, in radioastronomy, spectral line graphs are used to determine the kinematics or relativemotions of material at the center of a galaxy or surrounding a star as it is born.

Kirchhoff's law of radiation (G.R. Kirchhoff)The emissivity of a body is equal to its absorbance at the same temperature.

Kirchhoff's laws (G.R. Kirchhoff)Kirchhoff's first lawAn incandescent solid or gas under high pressure will produce a continuous spectrum.



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Kirchhoff's second lawA low-density gas will radiate an emission-line spectrum with an underlying emission continuum.

Kirchhoff's third lawContinuous radiation viewed through a low-density gas will produce an absorption-line spectrum.

LL0A representation of the luminosity of an object in terms of Solar luminosity. The average luminosity of theSun is about 4x1033 erg/sec. Astronomers often express units for other objects in terms of solar units...itmakes the resulting numbers smaller and easier to deal with.

Lagrange, Joseph (1736 - 1813)A French mathematician of the eighteenth century. His work Mecanique Analytique (AnalyticalMechanics; 1788) was a mathematical masterpiece. It contained clear, symmetrical notation and coveredalmost every area of pure mathematics. Lagrange developed the calculus of variations, established thetheory of differential equations, and provided many new solutions and theorems in number theory. Hisclassic Theorie des fonctions analytiques laid some of the foundations of group theory. Lagrange alsoinvented the method of solving differential equations known as variation of parameters. (54 k GIF)

Lagrange pointsPoints in the vicinity of two massive bodies (such as the Earth and the Moon) where each others'respective gravities balance. There are five, labeled L1 through L5. L1, L2, and L3 lie along the centerlinebetween the centers of mass between the two masses; L1 is on the inward side of the secondary, L2 is onthe outward side of the secondary; and L3 is on the outward side of the primary. L4 and L5, the so-calledTrojan points, lie along the orbit of the secondary around the primary, sixty degrees ahead and behind ofthe secondary.L1 through L3 are points of unstable equilibrium; any disturbance will move a test particle there out of theLagrange point. L4 and L5 are points of stable equilibrium, provided that the mass of the secondary is lessthan about 1/25.96 the mass of the primary. These points are stable because centrifugal pseudo-forceswork against gravity to cancel it out.

laserLaser is an acronym for Light Amplification by Stimulated Emission of Radiation. It's a device thatproduces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions tohigher levels so that when they return to lower energy levels they emit energy.

LHEALaboratory for High Energy Astrophysics (GSFC, Code 660)

lightElectromagnetic radiation that is visible to the human eye.

light curveA graph that displays the time variation in light or magnitude of a variable or eclipsing star.

Tell me about light curves



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light yearA unit of length used in astronomy which equals the distance light travels in a year. At the rate of 300,000kilometers per second (671 million miles per hour), 1 light-year is equivalent to 9.46053 x 1012 km,5,880,000,000,000 miles or 63,240 AU (see scientific notation).

limbThe outer edge of the apparent disk of a celestial body.

MM0A representation of the mass of an object in terms of Solar mass. The average mass of the Sun is about2x1033 grams. Astronomers often express units for other objects in terms of solar units...it makes theresulting numbers smaller and easier to deal with.

magnetic fieldA condition found in the region around a magnet or an electric current, characterized by the existence of adetectable magnetic force at every point in the region.

magnetic poleEither of two limited regions in a magnet at which the magnet's field is most intense.

magnetosphereThe region of space in which the magnetic field of an object (e.g., a star or planet) dominates the radiationpressure of the stellar wind to which it is exposed.

magnetotailThe portion of a planetary magnetosphere which is pushed in the direction of the solar wind.

magnitudeThe degree of brightness of a celestial body designated on a numerical scale, on which the brightest starhas magnitude -1.4 and the faintest visible star has magnitude 6, with the scale rule such that a decrease ofone unit represents an increase in apparent brightness by a factor of 2.512; also called apparent magnitude.

massA measure of the total amount of material in a body, defined either by the inertial properties of the body orby its gravitational influence on other bodies.

matterA word used for any kind of stuff which contains mass.

mega-tonA unit of energy used to describe nuclear warheads. The same amount energy as 1 million tons of TNT.

1 mega-ton = 4 x 1016 ergs = 4 x 109 joules.

meter; mThe fundamental SI unit of length, defined as the length of the path traveled by light in vacuum during aperiod of 1/299 792 458 s. A unit of length equal to about 39 inches. A kilometer is equal to 1000 meters.



microwaveElectromagnetic radiation which has a long wavelength (between 1 mm and 30 cm). Microwaves can beused to study the Universe, communicate with satellites in Earth orbit, and cook popcorn.

NnebulaA diffuse mass of interstellar dust and gas.

neutrinoA fundamental particle produced in massive numbers by the nuclear reactions in stars; they are very hardto detect because the vast majority of them pass completely through the Earth without interacting.

neutronA particle commonly found in the nucleus of atoms with approximately the mass of a proton, but zerocharge.

neutron starThe imploded core of a massive star produced by a supernova explosion. (typical mass of 1.4 times themass of the Sun, radius of about 5 miles, density of a neutron.) According to astronomer and author FrankShu, "A sugar cube of neutron-star stuff on Earth would weigh as much as all of humanity!" Neutron starscan be observed as pulsars.

Tell me about X-rays from neutron stars

Tell me about gamma-rays from black holes and neutron stars

Newton, Isaac 1642 - 1727English cleric and scientist; discovered the classical laws of motion and gravity; the bit with the apple isprobably apocryphal. (32 k GIF)

Newton's law of universal gravitation (Sir I. Newton)Two bodies attract each other with equal and opposite forces; the magnitude of this force is proportional tothe product of the two masses and is also proportional to the inverse square of the distance between thecenters of mass of the two bodies.

Newton's laws of motion (Sir I. Newton)Newton's first law of motionA body continues in its state of constant velocity (which may be zero) unless it is acted upon by anexternal force.

Newton's second law of motionFor an unbalanced force acting on a body, the acceleration produced is proportional to the force impressed;the constant of proportionality is the inertial mass of the body.

Newton's third law of motionIn a system where no external forces are present, every action force is always opposed by an equal andopposite reaction



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noiseThe random fluctuations that are always associated with a measurement that is repeated many times over.Noise appears in astronomical images as fluctuations in the image background. These fluctuations do notrepresent any real sources of light in the sky, but rather are caused by the imperfections of the telescope. Ifthe noise is too high, it may obscure the dimmest objects within the field of view.

nova (plural: novae)A star that experiences a sudden outburst of radiant energy, temporarily increasing its luminosity byhundreds to thousands of times before fading back to its original luminosity.

nuclear fusionA nuclear process whereby several small nuclei are combined to make a larger one whose mass is slightlysmaller than the sum of the small ones. The difference in mass is converted to energy by Einstein's famousequivalence "Energy = Mass times the Speed of Light squared". This is the source of the Sun's energy.

OoccultationThe blockage of light by the intervention of another object; a planet can occult (block) the light from adistant star.

opacityA property of matter that prevents light from passing through it; non-transparent. The opacity oropaqueness of something depends on the frequency of the light. For instance, the atmosphere of Venus istransparent to ultraviolet light, but is opaque to visual light.

orbitThe path of an object that is moving around a second object or point.

OSO 3Orbiting Solar Observatory 3

Tell me more about OSO 3

OSO 8Orbiting Solar Observatory 8

Tell me more about OSO 8

Ppair productionThe physical process whereby a gamma-ray photon, usually through an interaction with theelectromagnetic field of a nucleus, produces an electron and an anti-electron (positron). The originalphoton no longer exists, its energy having gone to the two resulting particles. The inverse process, pairannihilation, creates two gamma-ray photons from the mutual destruction of an electron/positron pair.

Tell me how astronomers use pair production



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parallaxThe angle between the two straight lines that join a celestial body to two different points of observation;e.g., two different points on the Earth as it moves through space.

parsecA large distance often used in astronomy, it is equal to 3.26 light years, or 3.1 x 1018 cm (see scientificnotation). A kiloparsec (kpc) is equal to 1000 parsecs. A megaparsec (Mpc) is equal to a million (106)parsecs.

An object is at a distance of 1 parsec from us if its parallax is 1 second of arc.

periapsisThe point in the orbit closest to the planet.

periastronThe point of closest approach of two stars, as in a binary star orbit.

perigeeThe point in the orbit closest to the Earth.

perihelionThe point in its orbit where a planet is closest to the Sun. when referring to objects orbiting the Earth theterm perigee is used; the term periapsis is used for orbits around other bodies. (opposite of aphelion)

photoelectric effectAn effect explained by A. Einstein which demonstrates that light seems to be made up of particles, orphotons. Light can excite electrons (called photoelectrons in this context) to be ejected from a metal. Lightwith a frequency below a certain threshold, at any intensity, will not cause any photoelectrons to beemitted from the metal. Above that frequency, photoelectrons are emitted in proportion to the intensity ofincident light.The reason is that a photon has energy in proportion to its wavelength, and the constant of proportionalityis the Planck constant. Below a certain frequency -- and thus below a certain energy -- the incident photonsdo not have enough energy to knock the photoelectrons out of the metal. Above that threshold energy,called the work function, photons will knock the photoelectrons out of the metal, in proportion to thenumber of photons (the intensity of the light). At higher frequencies and energies, the photoelectronsejected obtain a kinetic energy corresponding to the difference between the photon's energy and the workfunction.

piThe constant equal to the ratio of the circumference of a circle to its diameter, which is approximately3.141593.

Planck constant; hThe fundamental constant equal to the ratio of the energy of a quantum of energy to its frequency. It is thequantum of action. It has the value 6.626196 x 10-34 J s (see scientific notation).

Planck equationThe quantum mechanical equation relating the energy of a photon E to its frequency nu:



E = h x nu

planetary nebulaA shell of gas ejected from, and expanding about, a certain kind of extremely hot star.

plasmaA low-density gas in which the individual atoms are ionized (and therefore charged), even though the totalnumber of positive and negative charges is equal, maintaining an overall electrical neutrality.

pointingThe direction in the sky to which the telescope is pointed. Pointing also describes how accurately atelescope can be pointed toward a particular direction in the sky.

polarizationA special property of light; light has three properties, brightness, color and polarization. Polarization is acondition in which the planes of vibration of the various rays in a light beam are at least partially aligned.

positronThe antiparticle to the electron. The positron has most of the same characteristics as an electron except it ispositively charged.

protonA particle commonly found in the nucleus of atoms with a positive charge.

protostarVery dense regions (or cores) of molecular clouds where stars are in the process of forming.

Ptolemy (ca. 100-ca. 170)A.k.a.Claudius Ptolemaeus. Ptolemy believed the planets and Sun to orbit the Earth in the order Mercury,Venus, Sun, Mars, Jupiter, Saturn. This system became known as the Ptolemaic system and predicted thepositions of the planets accurately enough for naked-eye observations (although it made some ridiculouspredictions, such as that the distance to the moon should vary by a factor of two over its orbit). Heauthored a book called Mathematical Syntaxis (widely known as the Almagest). The Almagest included astar catalog containing 48 constellations, using the names we still use today. (10 k GIF)

pulsarA rotating neutron star which generates regular pulses of radiation. Pulsars were discovered byobservations at radio wavelengths but have since been observed at optical, X-ray, and gamma-rayenergies.

Tell me about pulsars!

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PVOPioneer Venus Orbiter

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QquasarA specific type of quasi-stellar source.

quasi-stellar source (QSS)Sometimes also called quasi-stellar object (QSO); A stellar-appearing object of very large redshift that is astrong source of radio waves; presumed to be extragalactic and highly luminous.

Rradial velocityThe speed at which an object is moving away or toward an observer. By observing spectral lines,astronomers can determine how fast objects are moving away from or toward us; however, these spectrallines cannot be used to measure how fast the objects are moving across the sky.

radian; radThe supplementary SI unit of angular measure, defined as the central angle of a circle whose subtended arcis equal to the radius of the circle.

radiationEnergy radiated in the form of waves or particles; photons.

radiation beltRegions of charged particles in a magnetosphere.

radioElectromagnetic radiation which has the lowest frequency, the longest wavelength, and is produced bycharged particles moving back and forth; the atmosphere of the Earth is transparent to radio waves withwavelengths from a few millimeters to about twenty meters.

Rayleigh criterion; resolving powerA criterion for how finely a set of optics may be able to distinguish. It begins with the assumption that thecentral ring of one image should fall on the first dark ring of another image; for an objective lens withdiameter d and employing light with a wavelength lambda (usually taken to be 560 nm), the resolvingpower is approximately given by

1.22 x lambda/d

Rayleigh-Taylor instabilitiesRayleigh-Taylor instabilities occur when a heavy (more dense) fluid is pushed against a light fluid -- liketrying to balance water on top of air by filling a glass 1/2 full and carefully turning it over.Rayleigh-Taylor instabilities are important in many astronomical objects, because the two fluids tradeplaces by sticking "fingers" into each other. These "fingers" can drag the magnetic field lines along withthem, thus both enhancing and aligning the magnetic field. This result is evident in the example of asupernova remnant in the diagram below, from Chevalier (1977):



red giantA star that has low surface temperature and a diameter that is large relative to the Sun.

redshiftAn apparent shift toward longer wavelengths of spectral lines in the radiation emitted by an object causedby the emitting object moving away from the observer. See also Doppler effect.

reflection lawFor a wavefront intersecting a reflecting surface, the angle of incidence is equal to the angle of reflection,in the same plane defined by the ray of incidence and the normal.

relativity principleThe principle, employed by Einstein's relativity theories, that the laws of physics are the same, at leastlocally, in all coordinate frames. This principle, along with the principle of the constancy of the speed oflight, constitutes the founding principles of special relativity.

relativity, theory ofMore accurately describes the motions of bodies in strong gravitational fields or at near the speed of lightthan Newtonian mechanics. All experiments done to date agree with relativity's predictions to a highdegree of accuracy. (Curiously, Einstein received the Nobel prize in 1921 not for Relativity but rather forhis 1905 work on the photoelectric effect.)

resolution (spatial)In astronomy, the ability of a telescope to differentiate between two objects in the sky which are separatedby a small angular distance. The closer two objects can be while still allowing the telescope to see them astwo distinct objects, the higher the resolution of the telescope.

resolution (spectral or frequency)Similar to spatial resolution except that it applies to frequency, spectral resolution is the ability of thetelescope to differentiate two light signals which differ in frequency by a small amount. The closer the twosignals are in frequency while still allowing the telescope to separate them as two distinct components, thehigher the spectral resolution of the telescope.

resonanceA relationship in which the orbital period of one body is related to that of another by a simple integerfraction, such as 1/2, 2/3, 3/5.

retrogradeThe rotation or orbital motion of an object in a clockwise direction when viewed from the north pole of theecliptic; moving in the opposite sense from the great majority of solar system bodies.

Right AscensionA coordinate which, along with declination, may be used to locate any position in the sky. Right ascension



is analogous to longitude for locating positions on the Earth.

Ritter, Johann Wilhelm (1776 - 1810)Ritter is credited with discovering and investigating the ultraviolet region of the electromagnetic spectrum.

Roche limitThe smallest distance from a planet or other body at which purely gravitational forces can hold together asatellite or secondary body of the same mean density as the primary; at less than this distance the tidalforces of the primary would break up the secondary.

Roche lobeThe volume around a star in a binary system in which, if you were to release a particle, it would fall backonto the surface of that star. A particle released above the Roche lobe of either star will, in general, occupythe `circumbinary' region that surrounds both stars. The point at which the Roche lobes of the two starstouch is called the inner Lagrangian or L1 point. If a star in a close binary system evolves to the point atwhich it `fills' its Roche lobe, theoretical calculations predict that material from this star will overflowboth onto the companion star (via the L1 point) and into the circumbinary environment.

Röntgen, Wilhelm Conrad (1845 - 1923)A German scientist who fortuitously discovered X-rays in 1895. (43 k GIF).

ROSATRöntgen Satellite

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SSAS-2The second Small Astronomy Satellite: a NASA satellite launched November 1972 with a missiondedicated to gamma-ray astronomy.

Tell me more about SAS-2

SAS-3The third Small Astronomy Satellite: a NASA satellite launched May 1975 to determine the location ofbright X-ray sources and search for X-ray novae and other transient phenomena.

Tell me more about SAS-3

satelliteA body that revolves around a larger body.

Schwarzschild radiusThe radius r of the event horizon for a Schwarzschild black hole.

scientific notationA compact format for writing very large or very small numbers, most often used in scientific fields. Thenotation separates a number into two parts: a decimal fraction, usually between 1 and 10, and a power often. Thus 1.23 x 104 means 1.23 times 10 to the fourth power or 12,300; 5.67 x 10-8 means 5.67 divided



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by 10 to the eighth power or 0.0000000567.

second; sThe fundamental SI unit of time, defined as the period of time equal to the duration of 9,192,631,770periods of the radiation corresponding to the transition between two hyperfine levels of the ground state ofthe cesium-133 atom. A nanosecond is equal to one-billionth (10-9) of a second.

semimajor axisThe semimajor axis of an ellipse (e.g. a planetary orbit) is 1/2 the length of the major axis which is asegment of a line passing thru the foci of the ellipse with endpoints on the ellipse itself. The semimajoraxis of a planetary orbit is also the average distance from the planet to its primary. The periapsis andapoapsis distances can be calculated from the semimajor axis and the eccentricity by

rp = a(1-e) and ra = a(1+e).

sensitivityA measure of how bright objects need to be in order for that telescope to detect these objects. A highlysensitive telescope can detect dim objects, while a telescope with low sensitivity can detect only brightones.

Seyfert galaxyA spiral galaxy whose nucleus shows bright emission lines; one of a class of galaxies first described by C.Seyfert.

shock waveA strong compression wave where there is a sudden change in gas velocity, density, pressure andtemperature.

singularityThe center of a black hole, where the curvature of spacetime is maximal. At the singularity, thegravitational tides diverge; no solid object can even theoretically survive hitting the singularity. Althoughsingularities generally predict inconsistencies in theory, singularities within black holes do not necessarilyimply that general relativity is incomplete so long as singularities are always surrounded by eventhorizons.A proper formulation of quantum gravity may well avoid the classical singularity at the centers of blackholes.

solar flaresViolent eruptions of gas on the Sun's surface.

solar massA unit of mass equivalent to the mass of the Sun. 1 solar mass = 1 Msun = 2 x 1033 grams.

special relativityThe physical theory of space and time developed by Albert Einstein, based on the postulates that all thelaws of physics are equally valid in all frames of reference moving at a uniform velocity and that the speedof light from a uniformly moving source is always the same, regardless of how fast or slow the source orits observer is moving. The theory has as consequences the relativistic mass increase of rapidly movingobjects, gravitational sources bending light, time dilatation, and the principle of mass-energy equivalence.



See also general relativity.

spectral lineLight given off at a specific frequency by an atom or molecule. Every different type of atom or moleculegives off light at its own unique set of frequencies; thus, astronomers can look for gas containing aparticular atom or molecule by tuning the telescope to one of its characteristic frequencies. For example,carbon monoxide (CO) has a spectral line at 115 Gigahertz (or a wavelength of 2.7 mm).

spectrometerThe instrument connected to a telescope that separates the light signals into different frequencies,producing a spectrum.

A Diversive Spectrometer is like a prism. It scatters the X-rays of different energies to different places.We measure the energy by noting where the X-rays go. A Non-Dispersive Spectrometer measures theenergy directly.

spectroscopyThe study of spectral lines from different atoms and molecules. Spectroscopy is an important part ofstudying the chemistry that goes on in stars and in interstellar clouds.

spectrum (plural: spectra)A plot of the intensity of light at different frequencies. Or the distribution of wavelengths and frequencies.

Tell me more about spectra

speed of light (in vacuo); cThe speed at which electromagnetic radiation propagates in a vacuum; it is defined as 299 792 458 m/s(186,000 miles/second). Einstein's Theory of Relativity implies that nothing can go faster than the speed oflight.

starA large ball of gas that creates and emits its own radiation.

star clusterA bunch of stars (ranging in number from a few to hundreds of thousands) which are bound to each otherby their mutual gravitational attraction.

Stefan-Boltzmann constant; sigma (Stefan, L. Boltzmann)The constant of proportionality present in the Stefan-Boltzmann law. It is equal to 5.6697 x 10-8 Watts persquare meter per degree Kelvin to the fourth power (see scientific notation).

Stefan-Boltzmann law (Stefan, L. Boltzmann)The radiated power P (rate of emission of electromagnetic energy) of a hot body is proportional to theradiating surface area, A, and the fourth power of the thermodynamic temperature, T. The constant ofproportionality is the Stefan-Boltzmann constant.

stellar classificationStars are given a designation consisting of a letter and a number according to the nature of their spectrallines which corresponds roughly to surface temperature. The classes are: O, B, A, F, G, K, and M; O starsare the hottest; M the coolest. The numbers are simply subdivisions of the major classes. The classes are



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oddly sequenced because they were assigned long ago before we understood their relationship totemperature. O and B stars are rare but very bright; M stars are numerous but dim. The Sun is designatedG2.

stellar windThe ejection of gas off the surface of a star. Many different types of stars, including our Sun, have stellarwinds; however, a star's wind is strongest near the end of its life when it has consumed most of its fuel.

steradian; srThe supplementary SI unit of solid angle defined as the solid central angle of a sphere that encloses asurface on the sphere equal to the square of the sphere's radius.

supernova (plural: supernovae)The death explosion of a massive star, resulting in a sharp increase in brightness followed by a gradualfading. At peak light output, supernova explosions can outshine a galaxy. The outer layers of theexploding star are blasted out in a radioactive cloud. This expanding cloud, visible long after the initialexplosion fades from view, forms a supernova remnant (SNR).

Tell me about X-rays from supernovae and their remnants

Tell me about gamma-rays from supernovae

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sunspotsCooler (and thus darker) regions on the sun where the magnetic field loops up out of the solar surface.

SXGThe Spectrum X-Gamma mission

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synchronous rotationSaid of a satellite if the period of its rotation about its axis is the same as the period of its orbit around itsprimary. This implies that the satellite always keeps the same hemisphere facing its primary (e.g. theMoon). It also implies that one hemisphere (the leading hemisphere) always faces in the direction of thesatellite's motion while the other (trailing) one always faces backward.

synchrotron radiationElectromagnetic radiation given off when very high energy electrons encounter magnetic fields.

Systéme Internationale d'Unités (SI)The coherent and rationalized system of units, derived from the MKS system (which itself is derived fromthe metric system), in common use in physics today. The fundamental SI unit of length is the meter, oftime is the second, and of mass is the kilogram.



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TTenmaThe second Japanese X-ray mission, also known as Astro-B.

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Thomson, William 1824 - 1907Also known as Lord Kelvin, the British physicist who developed the Kelvin scale of temperature and whosupervised the laying of a trans-Atlantic cable. (11 k GIF)

time dilationStretching of time produced by relativity. Time dilation is a predicted effect of the cosmological paradigm.

UUhuruNASA's first Small Astronomy Satellite, also known as SAS-1. Uhuru was launched from Kenya on 12December, 1970; The seventh anniversary of Kenya's independence. The satellite was named "Uhuru"(Swahili for "freedom") in honor of its launch date.

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ultravioletElectromagnetic radiation at wavelengths shorter than the violet end of visible light; the atmosphere of theEarth effectively blocks the transmission of most ultraviolet light.

universal constant of gravitation; GThe constant of proportionality in Newton's law of universal gravitation and which plays an analogous rolein A. Einstein's general relativity. It is equal to 6.664 x 10-11 newtons per square meter per kilogramsquared (see scientific notation).

VVela 5BUS Atomic Energy Commission (now the Department of Energy) satellite with an all-sky X-ray monitor

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The Venera satellite seriesThe Venera satellites were a series of probes (fly-bys and landers) sent by the Soviet Union to the planetVenus. Several Venera satellites carried high-energy astrophysics detectors.

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visibleElectromagnetic radiation at wavelengths which the human eye can see. We perceive this radiation as



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colors ranging from red (longer wavelengths; ~ 700 nanometers) to violet (shorter wavelengths; ~400nanometers.)

Wwave-particle dualityThe principle of quantum mechanics which implies that light (and, indeed, all other subatomic particles)sometimes act like a wave, and sometimes act like a particle, depending on the experiment you areperforming. For instance, low frequency electromagnetic radiation tends to act more like a wave than aparticle; high frequency electromagnetic radiation tends to act more like a particle than a wave.

wavelengthA property of a wave that gives the length between two peaks of the wave.

white dwarfA star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size. Typically, awhite dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to theSun's. This gives a white dwarf a density about 1 million times that of water!

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Wien's displacement lawFor a blackbody, the product of the wavelength corresponding to the maximum radiancy and thethermodynamic temperature is a constant. As a result, as the temperature rises, the maximum of the radiantenergy shifts toward the shorter wavelength (higher frequency and energy) end of the spectrum.

WWWThe World Wide Web -- a loose linkage of Internet sites which provide data and other services fromaround the world.

XX-rayElectromagnetic radiation of very short wavelength and very high-energy; X-rays have shorterwavelengths than ultraviolet light but longer wavelengths than cosmic rays.

XSELECTA high-level tool to manage the FTOOLs

XTEX-ray Timing Explorer, also known as the Rossi X-ray Timing Explorer (RXTE)

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Y

Z[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ]

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Black Holes Quiz

What would change if our Sun was suddenly replaced by a black hole of the same mass?

[A] Earth would be sucked into the black hole [B] The planets would no longer have the same orbit [C] Only the temperature on Earth would change

1.

Scientists only began to speculate on the existence of black holes in the twentieth century.

[A] True [B] False

2.

If a space probe could be sent into a black hole, it could transmit images back to Earth.

[A] True [B] False

3.

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Black Holes

Black holes are like vacuum cleaners... NOT!

A black hole has an "event horizon" which is a region inside of which you can't escape. If an objectcrosses the event horizon, it will invariably hit the singularity. As long as the object stays outside of thehorizon, it will not get sucked in. Outside of the horizon, the gravitational field surrounding a black hole isno different from the field surrounding any other object of the same mass. A black hole is not better thanany other object at "sucking in" distant objects.

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Imagine theUniverse! Lesson

Plans

The following Lesson Plans are available/under development:

Subject GradeLevel Math Standard Science Standard Title

Math 6-8

Patterns &FunctionsAlgebraStatistics

Science as InquiryWhat's theFrequency, RoyG. Biv?

Math 6-8AlgebraStatisticsFunctions

Science as InquiryMotions & Forces

Time ThatPeriod!

Math 6-8

NumberRelationshipsAlgebraPatterns &FunctionsStatistics

Science as InquiryOrigin/Evol. of Univ.TechnologyDesign/Understanding

How Big is ThatStar?

Adv Alg 9-12 Pattern Recognition Origin/Evol. of Univ. Stars and Slopes

Chemistry 11-12 Pattern RecognitionStruct./Prop. of MatterOrigin/Evol.of Univ.

SupernovaChemistry!

Imagine the Universe! Lesson Plans

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http://imagine.gsfc.nasa.gov/docs/teachers/lessons/time/time_period_cover.html

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http://imagine.gsfc.nasa.gov/docs/teachers/lessons/star_size/star_size_cover.html

http://imagine.gsfc.nasa.gov/docs/teachers/lessons/star_size/star_size_cover.html

http://imagine.gsfc.nasa.gov/docs/teachers/lessons/slopes/ss_title.html

http://imagine.gsfc.nasa.gov/docs/teachers/lessons/supernova/supernova_cover.html

http://imagine.gsfc.nasa.gov/docs/teachers/lessons/supernova/supernova_cover.html

Math 6-9 StatisticsTechnologyDesign/Understanding

Detective Digitand the SlapHappyComputer Caper

Math/Sp Sci 6-10

AlgebraStatisticsDiscreteMathematics

Science as InquiryEarth and Space ScienceScience and TechnologyHistory and Nature of Science

Get The Picture!

Math/Sp Sci 6-9

NumberRelationshipsPatterns &Functions

Science as InquiryOrigin/Evol. of Univ.TechnologyDesign/Understanding

Lotto or Life:What Are theChances?

Our lesson plans are being developed by both teachers and the Imagine the Universe! Team. If you havean idea you'd like to contribute, be sure to write us at [email protected].

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Other Resources (A-G)

H - R S - Z

ACTIVE GALACTIC NUCLEIhttp://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/quasars.html

This page contains information on quasars for the K-4 student, with a question at the end and linksto a glossary of defined terms.

●

http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level2/quasars.html

This page contains information on quasars written for the 5-8 grade student, with a question at theend and words linked to a glossary of terms.

●

Books

Gaustad, John & Zeilik, Michael, Astronomy: The Cosmic Perspective- second edition, John Wiley& Sons, Inc., 1990. This text was designed for an introductory astronomy course for upper highschool or undergraduate students who want a comprehensive view and understanding of modernastronomy, including active galaxies (see chapter26).

●

Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to beanother 'classic' X-ray astronomy text book. Includes discussion of active galaxies (see Chapter 13)at a level intended for the undergraduate science major, or above.

●

Kaufmann, William J. III, Universe, Freeman and Company, 1994. This book comes highlyrecommended from both students and scientists. It explains many concepts in astronomy fromcosmology to high-energy astrophysics, including information on active galaxies (see Chapter 27).Intended for the upper high school student with a strong science background and interest, or theundergraduate science major taking a basic astronomy course.

●

Mitton, Jacqueline & Simon, The Young Oxford Book of Astronomy, Oxford University Press, Inc.,1995. This book explains many concepts in astronomy from the Solar System, galaxies and theUniverse, including active galaxies. Intended for the middle or high school student.

●

Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe, Cambridge UniversityPress, 1995. Explains X-ray astronomy and astrophysics along with its most recent developments.Intended for the undergraduate science major, or above.

●

Magazine Articles

Bland-Hawthorne, Jonathan & Cecil, Gerald & Veilleux, Sylvain, "Colossa Galactic Explosions",Scientific American, February 1996, vol. 274, no. 2. Explains the formation and characteristics ofactive galaxies. Intended for the high school student interested in science, or above.

●

Clarke, Stuart, "Mystery at the Heart of Active Galaxies", Astronomy Now, February 1995, vol. 9,●


http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (1 of 9) [5/26/1999 11:25:28 AM]

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no. 2. Examines whether the many types of active galaxies (quasars, radio galaxies, and Seyferts),are all the same type of object but viewed from different angles. Intended for the high school studentinterested in science, or above.

**************************************************************ASTRONOMYSee GENERAL ASTRONOMY.

**************************************************************BINARY STAR SYSTEMS

http://www.isc.tamu.edu/~astro/binstar.html

This Web site contains much information and other links related to binary star systems. It ismaintained by Dan Bruton of the Department of Physics and Astronomy at Stephen F. Austin StateUniversity. For students in high school and above.

●

http://www.gettysburg.edu/project/physics/clea/CLEAdesc.html

This lab, 'Binary Star Light Curves', was produced by Project CLEA and examines how todetermine the period of a variable star from irregularly sampled measurements of its brightness.

The CLEA Project is associated with Gettysburg College, and develops laboratory exercises whichillustrate modern astronomical techniques using digital data and color images. They are suitable forhigh school and college classes at all levels, but come with defaults set for use in introductoryastronomy classes for non-science majors.

●

Books

Gaustad, John & Zeilik, Michael, Astronomy: The Cosmic Perspective- second edition, John Wiley& Sons, Inc., 1990. This text was designed for an introductory astronomy course for upper highschool or undergraduate students who want a comprehensive view and understanding of modernastronomy, including binary stars (see Chapter 17).

●

Giacconi, R. & Gursky, H., X-Ray Astronomy, D. Reidel Publishing Company. Known as a 'classic'X-ray astromomy text book. Includes discussion of binary stars (see Chapters 1 & 4) at a levelintended for the undergraduate science major, or above.

●

Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to beanother 'classic' X-ray astromomy text book. Includes discussion of binary stars (see Chapter 6) at alevel intended for the undergraduate science major, or above.

●

Kaufmann, William J. III, Universe, Freeman and Company, 1994. This book comes highlyrecommended from both students and scientists. It explains many concepts in astronomy fromcosmology to high-energy astrophysics, including information on binary stars (see Chapter 18).Intended for the upper high school student with a strong science background and interest, or theundergraduate science major taking a basic astronomy course.

●



http://www.isc.tamu.edu/~astro/binstar.html

http://www.gettysburg.edu/project/physics/clea/CLEAdesc.html

Mitton, Jacqueline & Simon, The Young Oxford Book of Astronomy, Oxford University Press, Inc.,1995. This book explains many concepts in astronomy from the Solar System, galaxies, and theUniverse, including binary stars. Intended for the middle or high school student.

●


●

**************************************************************BLACK HOLES

http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/black_holes.html

This page explains for the K-4 student what black holes are and how we know they exist.

●


This page contains information about black holes and how we know they exist, links to glossaryterms and a movie about a "Journey into a Blackhole."

●

http://jean-luc.ncsa.uiuc.edu/Movies/

This Web site has virtual reality and informational movies on black holes. This site is associatedwith NCSA, and is for students in middle school and above.

●

Books

Gaustad, John & Zeilik, Michael, Astronomy: The Cosmic Perspective- second edition, John Wiley& Sons, Inc., 1990. This text was designed for an introductory astronomy course for upper highschool or undergraduate students who want a comprehensive view and understanding of modernastronomy, including black holes (see Chapters 20 & 21).

●

Giacconi, R. & Gursky, H., X-Ray Astronomy, D. Reidel Publishing Company. Known as a 'classic'X-ray astromomy text book. Includes discussion of black holes (see Chapters 4 & 6) at a levelintended for the undergraduate science major, or above.

●

Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to beanother 'classic' X-ray astromomy text book. Includes discussion of black holes (see Chapter 7) at alevel intended for the undergraduate science major, or above.

●

Kaufmann, William J. III, Universe, Freeman and Company, 1994. This book comes highlyrecommended from both students and scientists. It explains many concepts in astronomy fromcosmology to high-energy astrophysics, including information on black holes (see Chapter 24).Intended for the upper high school student with a strong science background and interest, or theundergraduate science major taking a basic astronomy course.

●

Levy, David H., A Nature Company Guide: Skywatching, Time-Life Books, 1995. This bookprovides a general overview and discussion of astronomical objects, including black holes. Forstudents in middle school or above.

●

Mitton, Jacqueline & Simon, The Young Oxford Book of Astronomy, Oxford University Press, Inc.,1995. This book explains many concepts in astronomy from the Solar System, galaxies, and the

●





http://jean-luc.ncsa.uiuc.edu/Movies/

Universe, including black holes. Intended for the middle or high school student.

Rosen, Sidney, How Far is a Star?, Carolrhoda Books, Inc.,1992. With cartoon characters leadingthe way, you'll find out about our Sun and other stars (including black holes) in thisquestion-and-answer book. Intended for students in elementary school.

●


●

Voyage Through the Universe: Stars, Time-Life Books. This volume is one of a series thatexamines the Universe in all its aspects. General information for the upper high school student (andabove), related to black holes, will be found in the 'Neutron Stars and Black Holes' chapter.

●

Magazine Articles

Charles, Philip A. & Wagner, R. Mark, "Black Holes in Binary Stars: Weighing the Evidence", Skyand Telescope, May 1996, vol. 91, no. 5. >From this article, one can understand that by makingX-ray observations, astronomers are sometimes able to detect black holes (especially when coupledto a normal star in a binary system). Intended for the high school student interested in science, orabove.

●

Schulkin, Bonnie, "Does a Monster Lurk Closeby", Astronomy, September 1997, vol. 25, no. 9.Describes the possibility of a massive black hole existing at the heart of our Milky Way Galaxy.Intended for the high school student interested in science, or above.

●

Berstein, Jeremy, "The Reluctant Father of Black Holes", Scientific American, June 1996, vol. 274,no. 6. Discusses the details of how Einstein's equations of gravity are the foundation of the modernview of black holes. Intended for the high school student who is interested in science, and above.

●

**************************************************************CATACLYSMIC VARIABLES

http://www.kusastro.kyoto-u.ac.jp/vsnet/index.html

This Web site contains basic information on CVs, at a level appropriate for high school students andtheir teachers. Also included are links to research sites, conference notices, etc.

●

http://sousun1.phys.soton.ac.uk/~trm/cv_picture.html

This Web site gives a nice description along with some model diagrams of CV system evolution.Might be useful to an advanced high school student, but clearly aimed at a college level.

●

Magazine Articles

"Accretion Disks in Interacting Binary Stars" by Canizzo & Kaitchuck, 1992, Scientific American,January, 92-99.

●

"Henry Norris Russel Prize Lecture of the American Astronomical Society: Fifty years of novae" byPayne-Gaposchkin, 1977, AJ 82, 665-673. Even though this appeared in a professional journal, it isappropriate for serious amateur astronomers and undergraduates majoring in physical sciences.

●



http://www.kusastro.kyoto-u.ac.jp/vsnet/index.html

http://sousun1.phys.soton.ac.uk/~trm/cv_picture.html

**************************************************************COMETS

Books

Rosen, Sidney, Can You Hitch a Ride on a Comet?, Carolrhoda Books, Inc.,1992. With cartooncharacters leading the way, you'll find out all kinds of information about comets in thisquestion-and-answer book. Intended for students in elementary school.

●

**************************************************************COSMIC RAYS

http://helios.gsfc.nasa.gov

Produced by the ACE project at NASA Goddard Space Flight Center, this site is designed toincrease interest in cosmic rays and heliospheric science. (The heliosphere is the HUGE area inspace affected by the Sun.) It also includes some astrophysics basics, a glossary, a history of cosmicray studies, and the chance to "Ask a Physicist." High school level or above.

●

**************************************************************DARK MATTER

http://heasarc.gsfc.nasa.gov/Images/rosat/display/darkmatter.html

This is a display from ROSAT. It has some information about dark matter in a short paragraph aswell as data from the satellite. It is a good resource for middle/high school students and teachers.

●

http://physics7.berkeley.edu/darkmat/dm.html

This is a basic description of what dark matter is, why we think it exists, and why it is important forcosmology. It contains a lot of text, but is understandable and defines the terms that are used. Linksto more information (including books!) are given at the end. Appropriate for highschool/undergraduate physics students.

●

http://web.mit.edu/afs/athena.mit.edu/user/r/e/redingtn/www/netadv/dkmatter/gen.html

This is a list of links to dark matter pages. The list is divided into sections based on the difficultylevel of the referenced sites.

●

http://web.mit.edu/afs/athena.mit.edu/user/r/e/redingtn/www/netadv/dkmatter.html

This is the basic description page that goes along with the links above. It is accessible to highschool/undergraduates.

●

http://physics7.berkeley.edu/darkmat/essay.html

This is an essay on dark matter including its effects at different size scales, evidence for and against

●



http://helios.gsfc.nasa.gov/

http://heasarc.gsfc.nasa.gov/Images/rosat/display/darkmatter.html

http://physics7.berkeley.edu/darkmat/dm.html

http://web.mit.edu/afs/athena.mit.edu/user/r/e/redingtn/www/netadv/dkmatter/gen.html

http://web.mit.edu/afs/athena.mit.edu/user/r/e/redingtn/www/netadv/dkmatter.html

http://physics7.berkeley.edu/darkmat/essay.html

it, how much we expect there to be, etc. VERY LONG, but very thorough.

http://pilot.msu.edu/user/vanhoose/astro/0023.html

HST results (1994) showing that red dwarfs do not make up the bulk of the dark matter. This readslike a NASA press report,but anyone who can read a newspaper would get something out of thisarticle. Has background information, too.

●

http://zebu.uoregon.edu/text/darkmatter.txt

This is "text only". Covers important points and also fairly recent discoveries which contribute toour understanding of dark matter. Accessible for high school.

●

Magazine Articles

"Dark Matter and the Origin of Cosmic Structure", Sky and Telescope. October 1994. Goodresource for high school aged students and teachers. Back issues are $4.50 within the USA.Instructions on how to order can be found at: http://www.skypub.com/s_t/s_tback.html#order.

●

"Searching for Dark Matter", Sky and Telescope. January 1994. High school.●

Books

"Invisible Matter and the Fate of the Universe", by Barry Parker; a decent non-technical book ondark matter, although a little dated (1989)

●

**************************************************************DIFFUSE BACKGROUND

http://lheawww.gsfc.nasa.gov/users/snowden/shadow/shadow.html

This site contains historical background, current models, pictures, and relevant papers on soft X-raydiffuse background. It is associated with the Laboratory for High Energy Astrophysics, and isintended for college level science majors.

●

Books

Giacconi, R. & Gursky, H., X-Ray Astronomy, D. Reidel Publishing Company. Known as a 'classic'X-ray astromomy text book. Includes discussion of diffuse background (see Chapter 10) at a levelintended for the undergraduate science major, or above.

●

Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to beanother 'classic' X-ray astromomy text book. Includes discussion of diffuse background (see Chapter15) at a level intended for the undergraduate science major, or above.

●


●



http://pilot.msu.edu/user/vanhoose/astro/0023.html

http://zebu.uoregon.edu/text/darkmatter.txt

http://www.skypub.com/s_t/s_tback.html#order

http://lheawww.gsfc.nasa.gov/users/snowden/shadow/shadow.html

**************************************************************EARTH

http://www.globe.gov/

Global Learning and Observations to Benefit the Environment (GLOBE) is a worldwide network ofstudents, teachers, and scientists working together to study and understand the global environment.

●

**************************************************************GALAXIES

Books

Rosen, Sidney, Which Way to the Milkyway?, Carolrhoda Books, Inc.,1992. With cartooncharacters leading the way, you'll find out much about our Milky Way and other galaxies in thisquestion-and-answer book. Intended for students in elementary school.

●

**************************************************************GAMMA RAY BURSTS

http://www.astro.ucla.edu/irlab/grb.htm

This is a thorough history and description of the current theory of gamma-ray bursters. Goodgeneral information presented at a level appropriate for high school students.

●

http://www.lucifer.com/if-lists/if-sci/0035.html

This is a detailed explanation of the reasoning and evidence for belief that gamma-ray bursters arenot limited to the Milky Way. A good jumping off point for reports and such for high schoolstudents.

●

Magazine Articles

"Unsolved Mysteries of the Sun -- Part II; Gamma-Ray Bursts: A Growing Enigma" Sky andTelescope. September 1996. Aimed at the mature astronomer and a good resource for high schoolaged students and teachers.

●

"A New View to a Kill", by Peter Kurczynski. Mercury Magazine. Volume 27, #4. July/August1997. For the first time since gamma-ray bursts were discovered, these elusive high-energy flasheshave shown up in X-ray and optical images. Written for the motivated non-expert. Appropriate forhigh school/undergraduates.

●

"The Mother of All Fireworks", by Peter Kurczynski. Mercury Magazine. Volume 25 #5.September/October 1996. Spy satellites saw them first. They blast with the energy of a supernova.And every time astronomers think they know what they are, gamma-ray bursts reveal a surprise.

●

Fishman, Gerald J. & Harmann, Dieter H., "Gamma-Ray Bursts", Scientific American, January●



http://www.globe.gov/

http://www.astro.ucla.edu/irlab/grb.htm

http://www.lucifer.com/if-lists/if-sci/0035.html

1997, vol. 277, no. 1. Explains one of the most powerful explosions in the Universe. Intended forthe high school student interested in science, or above.

**************************************************************GAMMA-RAY DETECTORS


This Web site is the Compton Gamma-Ray Astronomy home page. It has a lot of informationpresented in a fairly straightforward way. Includes images, new discoveries, and specs on theinstruments. Unfortunately information on many levels is all mixed in together, from middle schoolto college.

●

**************************************************************GENERAL ASTRONOMY

http://starchild.gsfc.nasa.gov

The Imagine the Universe! counterpart for younger astronomers. This site is aimed at studentsgrades K-4 (designated Level 1) and 5-8 (designated Level 2). It contains easy-to-understandinformation about the solar system, the Universe, and other "space stuff" as well as activities,movies, puzzles, etc. Each topic has a short quiz at the end. This site, written by middle schoolteachers, is a great educational resource with lots of fun!

●

http://cnde.iastate.edu/staff/jtroeger/astronomy.html

This Web site is an astronomy course for middle/high school students using the Internet.

●

http://heasarc.gsfc.nasa.gov/docs/www_info/webstars.html

WebStars: Astrophysics in Cyberspace, a large list of other astronomy sites, with short descriptions.

●

http://antwrp.gsfc.nasa.gov/apod/astropix.html

Astronomy Picture of the Day: Each day a different image or photograph of our fascinatingUniverse is featured, along with a brief explanation written by a professional astronomer. Archivedpictures (sorted by date and by subject) go back to June, 1995. The text is very informative andcontains useful links to related information. Accessible for high school students and above.

●

**************************************************************

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http://starchild.gsfc.nasa.gov/

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http://antwrp.gsfc.nasa.gov/apod/astropix.html

Welcome to Imagine the Universe!A service of the High-Energy Astrophysics Learning Center

This site is dedicated to a discussion about our Universe... what we know about it, how it is evolving, andthe kinds of objects and phenomena it contains. Just as importantly, we also discuss how scientists knowwhat they know, what mysteries remain, and how they might one day find the answers to these questions.

This site is intended primarily for ages 14 and up. If you are interested in a lower level, more basicdiscussion about astronomy and space exploration, try our StarChild site. It may have just what you arelooking for!

You will navigate around our site using a series of buttons at the bottom of each page. This is your chanceto learn about the navigation buttons!

Any time you see , you can go to a new window showing the Math and ScienceEducation Standards for that page. When you are done viewing the standards, close that window to returnto the page you were on previously.

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Lots of people have all sorts of questions about things such as black holes, quasars, dark matter, and somuch more. But they don't ask because they don't know who to ask or don't want to look silly or aren't surehow to ask.

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But wait - here are some things you need to know!Younger readers (ages 4-14) may find the information they need about general astronomy and spaceflighton StarChild.

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These are longer explanations that try to answer many questions that we have received on the same (orrelated) topic.

Are we going to be hit by an asteroid?●

The Cosmic Distance Scale●

Primary Areas of Interest and Expertise:

Astronomy as a Profession

Binary Star Systems

Black Holes

Cosmology

Dark Matter

Galaxies

Neutron stars

Quasars

Relativity

Stars

Supernovae and Their Remnants

X-rays and Gamma-rays

We also answer questions in other categories.

● Submit Your Question

It usually takes 1-3 weeks for our volunteers to answer a question. If we are especially busy, it maytake longer.



http://imagine.gsfc.nasa.gov/docs/ask_astro/new_planets.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/whatsnew.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/danger.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/cosmic/cosmic.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/profession.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/binary.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/black_holes.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/cosmology.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/dark_matter.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/galaxies.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/neutron_star.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/quasar.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/relativity.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/stars.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/snr.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/xrays.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/sub.html#other

http://imagine.gsfc.nasa.gov/docs/ask_astro/guidelines.html

Imagine!Homepage

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Imagine the Science!The Science Section of Imagine the Universe!

Here you can find all sorts of information related to what we know about the structures in, and theevolution of, our Universe. There is information about how we know what we know, what mysteries stillremain, and how scientists hope to discover the answers to some of these puzzles. The Universe weexplore here is the Universe of pulsars, black holes, supernovae, gamma-ray bursts, dark matter, andquasars. It is a Universe of extremes -- extremely high energies, extremely high densities, extremely highpressures, extremely intense magnetic fields. It is a Universe we can use as the ultimate laboratory,achieving physical conditions which we cannot replicate here on Earth, which allow us to test ourunderstanding and application the laws of physics. It is an amazing Universe, just Imagine!

Imagine What We Know

Active Galaxies & Quasars Binary Systems Black Holes

Cataclysmic Variables Dark Matter Diffuse Background

The Electromagnetic Spectrum Gamma-Ray Astronomy Gamma-Ray Bursts

Multiwavelength Astronomy Pulsars Stars

The Sun Supernovae White Dwarfs

X-ray Astronomy X-ray Transients

Science Links

http://imagine.gsfc.nasa.gov/docs/science/science.html (1 of 2) [5/26/1999 11:26:03 AM]

http://imagine.gsfc.nasa.gov/docs/introduction/active_galaxies.html

http://imagine.gsfc.nasa.gov/docs/introduction/binaries.html

http://imagine.gsfc.nasa.gov/docs/introduction/black_holes.html

http://imagine.gsfc.nasa.gov/docs/introduction/cataclysmic_variables.html

http://imagine.gsfc.nasa.gov/docs/introduction/dark_matter.html

http://imagine.gsfc.nasa.gov/docs/introduction/diffuse_background.html

http://imagine.gsfc.nasa.gov/docs/introduction/emspectrum.html

http://imagine.gsfc.nasa.gov/docs/introduction/gamma_information.html

http://imagine.gsfc.nasa.gov/docs/introduction/bursts.html

http://imagine.gsfc.nasa.gov/docs/introduction/multiwavelength.html

http://imagine.gsfc.nasa.gov/docs/introduction/pulsars.html

http://imagine.gsfc.nasa.gov/docs/introduction/stars.html

http://imagine.gsfc.nasa.gov/docs/introduction/sun.html

http://imagine.gsfc.nasa.gov/docs/introduction/supernovae.html

http://imagine.gsfc.nasa.gov/docs/introduction/dwarfs.html

http://imagine.gsfc.nasa.gov/docs/introduction/xray_information.html

http://imagine.gsfc.nasa.gov/docs/introduction/xray_tran_intro.html

Imagine How We Know It

Gamma-Ray Generation Gamma-Ray Telescopes & Detectors Lightcurves, Spectra, and Images

Spectral Analysis Timing Analysis X-ray Detectors

X-ray Generation X-ray Telescopes

Imagine the Remaining Mysteries

Origin and Destiny of theUniverse

The Lumpy Universe Evolution of Known Structures

Evolution of GalaxiesGrowth of Massive BlackHoles

Development of Elements in theUniverse

Matter in Extreme Conditions Validation of Relativity Nature of Dark Matter

Imagine Finding the Answers

Higher Resolution Greater Collection Area Exploring New Wavelengths

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Science Links

http://imagine.gsfc.nasa.gov/docs/science/science.html (2 of 2) [5/26/1999 11:26:03 AM]

http://imagine.gsfc.nasa.gov/docs/introduction/gamma_generation.html

http://imagine.gsfc.nasa.gov/docs/introduction/gamma_detectors.html

http://imagine.gsfc.nasa.gov/docs/introduction/analysis.html

http://imagine.gsfc.nasa.gov/docs/introduction/spectral.html

http://imagine.gsfc.nasa.gov/docs/introduction/timing.html

http://imagine.gsfc.nasa.gov/docs/introduction/xray_detectors.html

http://imagine.gsfc.nasa.gov/docs/introduction/xray_generation.html

http://imagine.gsfc.nasa.gov/docs/introduction/xray_telescopes.html

http://imagine.gsfc.nasa.gov/docs/introduction/origin_destiny.html

http://imagine.gsfc.nasa.gov/docs/introduction/origin_destiny.html

http://imagine.gsfc.nasa.gov/docs/introduction/lumpy.html

http://imagine.gsfc.nasa.gov/docs/introduction/structures.html

http://imagine.gsfc.nasa.gov/docs/introduction/galaxies.html

http://imagine.gsfc.nasa.gov/docs/introduction/massive.html

http://imagine.gsfc.nasa.gov/docs/introduction/massive.html

http://imagine.gsfc.nasa.gov/docs/introduction/composition.html

http://imagine.gsfc.nasa.gov/docs/introduction/composition.html

http://imagine.gsfc.nasa.gov/docs/introduction/conditions.html

http://imagine.gsfc.nasa.gov/docs/introduction/relativity.html

http://imagine.gsfc.nasa.gov/docs/introduction/nature.html









Satellites and Data

Welcome to an Introduction to Satellites and their Data. Here you can find out all about the satellites, theirmissions, the kinds of data they produced, and the exciting discoveries derived from those data.

The SatellitesProbing the structure and evolution of our Universe and the objects its contains requires, in general, thatwe make our observations above Earth's absorbing atmosphere. Starting with sounding rocket flights in thelate 1940s, scientists have been able to develop ever-better instruments to probe deeper into space andfiner into the details of our cosmos. This section will allow you to learn about the satellites and missionswhich have provided scientists the foundation of "what we know".

Tell Me about X-ray Astronomy Satellites & Missions

Tell Me about Gamma-ray Astronomy Satellites & Missions

Tell Me about Cosmic Ray Satellites & Missions

The DataThe information, or data, about our Universe measured by the instruments aboard satellites are transferredto the ground and analyzed by scientists. The data can arrive in many forms and much processing isusually required before it can be used to "do science". This section will discuss the data, the typicalprocessing, the final data archive, the scientific analysis process, and the final scientific results.

Tell Me about Getting Data from the Satellite to the Ground

Tell Me about Data Processing

Tell Me about Data Archives

Tell Me about Data Analysis

Tell Me about Scientific Results from Data

Imagine!Homepage

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Satellites, Data, and Software

http://imagine.gsfc.nasa.gov/docs/sats_n_data/sats_n_data.html (1 of 2) [5/26/1999 11:26:06 AM]

http://imagine.gsfc.nasa.gov/docs/sats_n_data/xray_missions.html

http://imagine.gsfc.nasa.gov/docs/sats_n_data/gamma_missions.html

http://imagine.gsfc.nasa.gov/docs/sats_n_data/cosmic_missions.html




Satellites, Data, and Software

http://imagine.gsfc.nasa.gov/docs/sats_n_data/sats_n_data.html (2 of 2) [5/26/1999 11:26:06 AM]









Pathways to AstronomyEducation Resources

The Universe is a very big place...and there are many ways to explore it. In this Section of Imagine the Universe!,we will provide you with the pathways to other World-Wide Web sites, posters, books, magazines, slide sets,movies, and whatever else we could find that we think you'll find useful.

Show me the topics:

[A - G] [H - R] [S - Z]

Active Galactic NucleiAstronomy

Binary Star SystemsBlack Holes

Cataclysmic VariablesComets

Cosmic RaysDark Matter

Diffuse BackgroundEarth

GalaxiesGamma-ray Bursts

Gamma-ray DetectorsGeneral Astronomy

History of Gamma-ray AstronomyHistory of X-ray Astronomy

InfraredMultiwavelength Astronomy

Neutron StarsPulsarsQuasarsRadio

StarsStellar Coronae

SunSN And Their Remnants

UltravioletVisible

White DwarfsX-ray Astronomy

X-ray BinariesX-ray Telescopes And Detectors

X-ray Transients

Other Good Resources

http://imagine.gsfc.nasa.gov/docs/resources/pathways.html (1 of 2) [5/26/1999 11:26:11 AM]

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#history_gamma

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#history_xray

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#infrared

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#multiwavelength

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#neutron_stars

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#pulsars

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#quasars

http://imagine.gsfc.nasa.gov/docs/resources/resources_h.html#radio

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#stars

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#stellar_coronae

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#sun

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#sn

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#ultraviolet

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#visible

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#white_dwarfs

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#xray

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#xray_binaries

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#xray_telescopes

http://imagine.gsfc.nasa.gov/docs/resources/resources_s.html#xray_transients

Imagine!Homepage

Imagine!Feedback

Ask aNASA

Scientist

ImagineScience!

Satellites& Data

OtherGood

Resources

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Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center(HEASARC), Dr. Nicholas E. White (Director), within the Laboratory for High Energy Astrophysics (LHEA) atNASA/ GSFC.


Comments or Feedback about our site can be sent to: [email protected]. Science-related questionsshould be directed to Ask a NASA Scientist .

Other Good Resources

http://imagine.gsfc.nasa.gov/docs/resources/pathways.html (2 of 2) [5/26/1999 11:26:11 AM]








The Teacher'sCorner

Want to "Know What our Long-Term Plans Are and Where You Might See Us?"

Currently, our Teacher Resources include:

Lesson Plans

Adopt an Astronomer

Information about NASA education initiatives and opportunities

Other Education Resources about Imagine the Universe! topics

Other Good General Science Education Web Sites

Life Cycles of Stars - Information and Activity Booklets

The Anatomy of Black Holes - Information and Activity Booklets

Send us your comments [email protected]

The Teacher's Corner: Multidisciplinary Classroom Activities

http://imagine.gsfc.nasa.gov/docs/teachers/teachers_corner.html (1 of 2) [5/26/1999 11:26:15 AM]

http://imagine.gsfc.nasa.gov/docs/teachers/long_term.html

http://imagine.gsfc.nasa.gov/docs/teachers/adopt_astronomer.html

http://imagine.gsfc.nasa.gov/docs/teachers/opportunities.html

http://imagine.gsfc.nasa.gov/docs/teachers/best.html

http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/stars.html

http://imagine.gsfc.nasa.gov/docs/teachers/blackholes/blackholes.html

http://imagine.gsfc.nasa.gov/cgi-bin/teacher_feeback.pl

http://imagine.gsfc.nasa.gov/cgi-bin/teacher_feedback.pl

http://imagine.gsfc.nasa.gov/cgi-bin/teacher_feedback.pl

Imagine!Homepage

Imagine!Feedback

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The Teacher's Corner: Multidisciplinary Classroom Activities

http://imagine.gsfc.nasa.gov/docs/teachers/teachers_corner.html (2 of 2) [5/26/1999 11:26:15 AM]









X-Ray Astronomy Program Working Group

[HEASARC Information] [Archive] [Software] [Calibration][What's New] [Links] [Public Outreach & Education]

[Missions] [ASCA] [BeppoSAX] [CGRO] [ROSAT] [RXTE] [EUVE][Astro-E] [AXAF] [Integral] [XMM] [Spectrum-X-Gamma]

HEASARC/GSFC Home Page

http://heasarc.gsfc.nasa.gov/ (1 of 2) [5/26/1999 11:26:37 AM]

http://heasarc.gsfc.nasa.gov/docs/xapwg.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_snr.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_blackhole.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_binary.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_outreach.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_links.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_whatsnew.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_calib.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_sw.html


http://heasarc.gsfc.nasa.gov/docs/xmm/xmmgof.html

http://obswww.unige.ch/isdc/

http://asc.harvard.edu/

http://heasarc.gsfc.nasa.gov/docs/astroe/astroegof.html

http://heasarc.gsfc.nasa.gov/docs/euve/euvegof.html

http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html

http://heasarc.gsfc.nasa.gov/docs/rosat/rosgof.html

http://cossc.gsfc.nasa.gov/cossc/cossc.html

http://heasarc.gsfc.nasa.gov/docs/sax/saxgof.html

http://heasarc.gsfc.nasa.gov/docs/asca/ascagof.html

http://heasarc.gsfc.nasa.gov/docs/heasarc/missions.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_archive.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_info.html

http://www.nasa.gov/

http://heasarc.gsfc.nasa.gov/docs/frames/mb_search.html

http://heasarc.gsfc.nasa.gov/docs/frames/mb_feedback.html

http://heasarc.gsfc.nasa.gov/docs/frames/mb_tour.html

http://imagine.gsfc.nasa.gov/

http://heasarc.gsfc.nasa.gov/docs/frames/mb_webstars.html

http://heasarc.gsfc.nasa.gov/docs/frames/mb_resources.html

http://heasarc.gsfc.nasa.gov/docs/frames/mb_tools.html

http://skyview.gsfc.nasa.gov/skyview.html

http://heasarc.gsfc.nasa.gov/ab/

http://heasarc.gsfc.nasa.gov/docs/frames/mb_argus.html

http://heasarc.gsfc.nasa.gov/docs/frames/mb_w3browse.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_info.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_archive.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_sw.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_calib.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_whatsnew.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_links.html

http://heasarc.gsfc.nasa.gov/docs/frames/hhp_outreach.html


http://heasarc.gsfc.nasa.gov/docs/asca/ascagof.html

http://heasarc.gsfc.nasa.gov/docs/sax/saxgof.html

http://cossc.gsfc.nasa.gov/cossc/cossc.html

http://heasarc.gsfc.nasa.gov/docs/rosat/rosgof.html

http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html

http://heasarc.gsfc.nasa.gov/docs/euve/euvegof.html

http://heasarc.gsfc.nasa.gov/docs/astroe/astroegof.html


http://obswww.unige.ch/isdc/



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This file was last modified on Tuesday, 22-Dec-1998 14:51:28 EST

Part of the NASA OSS Structure and Evolution of the Universe theme.

A service of the Laboratory for High Energy Astrophysics (LHEA) at NASA/ GSFC

HEASARC Director: Dr. Nicholas E. White, [email protected] Rep: Sherri Calvo, [email protected]/Comments/FeedbackNASA's Privacy StatementTell me about black holes, astronomy, and more!

HEASARC/GSFC Home Page

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Dr. Nicholas White -HEASARC Director

Office: GSFC Building 2, 250●

Address: Code 662, GSFC, Greenbelt, MD, 20771, USA●

Phone: 301 286 8443●

Fax: 301 286 1684●

e-mail: [email protected]●

Home Page (Papers, publications and pictures)●

Curriculum Vitae●

A Message from the DirectorFollowing recommendations from the NASA advisory committees, the HEASARC was established in1990 to archive the data from X-ray and Gamma-ray astronomy missions including the ASCA, Compton

Dr. Nicholas White

http://heasarc.gsfc.nasa.gov/docs/bios/white.html (1 of 2) [5/26/1999 11:26:51 AM]


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http://asca.gsfc.nasa.gov/


GRO, ROSAT, XTE , EUVE and BeppoSAX observatories. HEASARC is also responsible for restoringdatasets from historic missions flown since the field of X-ray and Gamma-ray astronomy began in the1960s. We retain and distribute not only all of the data from NASAs high energy astrophysics missions,but also that from European and Japanese satellites. Currently the HEASARC data holding total over 1Terrabyte of data, with all of these data available for immediate ftp download via our W3Browse andSkyview user interfaces. The HEASARC is currently one of the largest online astronomy archives. Butthe HEASARC is more than just an archive for X-ray and Gamma-ray astronomy data. To effectively usethese multi-mission data it is important to provide a mission independent infrastructure for their accessand analysis. To do this the HEASARC has pioneered the setting of software and data format standardsacross many different missions.

This multimission approach both saves money through the reuse of software and promotes amulti-mission/multi-wavelength approach to the data analysis. As we look forward to the major X-rayand Gamma-ray observatories Chandra Observatory, XMM, Astro-E and Integral to be launched aroundthe turn of the century, the infrastructure laid down by the HEASARC provides a sound basis for thefuture. Over the coming years we plan to build on the current infrastructure to provide more value-addedinterfaces to the archive, that will provide on demand higher level products in the most usefull formrequired.

As Director of the HEASARC I am responsible for all aspects of the HEASARC operations. I welcomeand encourage comments (both positive and negative) from our community of users. The HEASARCUsers Group (HUG) meets once per year to give me advice and feedback on the HEASARC activities. Ialso monitor the Feedback e-mail line and I encourage you to send in comments and suggestions.

About the Director

Return to the OGIP Staff page

Page Last Update: Monday, 1-Jun-1999

Part of the NASA OSS Structure and Evolution of the Universe theme.

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