astronomy - sun and stars

SUN(The Closest

Star)

SIZE:Angula

r size :0.5˚

Distance : 150 million km

Diameter: 1, 392, 000 km

If you think of the Sun as a basketball, the Earth would only be the size of the head of a pin.

If the Sun were a hallow ball, it would take about one million Earths to fill it.

The Sun is 109 times wider than the Earth. So 109 Earths would fit across the diameter of the Sun.

The mass of the Sun (the amount of stuff) is 330,000 times that of the Earth.

The mass of the Sun accounts for 99.86% of the total mass (total amount of stuff) in the solar system.

COMPOSITION Relative

number of atomsH – 94%He – 6%

Percentage by mass

The Sun’s Interior1.Core2.Radiative Zone3.Convection Zone

The core is at the center. It is the hottest region, where the nuclear fusion reactions that power the Sun occur.

Radiative (or radiation) zone. Its name is derived from the way energy is carried outward through this layer, carried by photons as thermal radiation.

Convective (or convection) zone. It is also named after the dominant mode of energy flow in this layer; heat moves upward via roiling convection, much like the bubbling motion in a pot of boiling oatmeal.

The Sun’s SurfacePhotosphere Light sphere The boundary

between the Sun's interior and the solar atmosphere

500 km thick Temperature = 5840

KelvinMeasuring the Sun’s temperature: Wien’s law Flux of energy

Wien’s Law

Flux of energy

Features on the PhotosphereSunspots + granulation in the photosphere (courtesy of Peter N. Brandt)

Galileo discovered that the Sun’s surface is sprinkled with small dark regions called sunspots.

Sunspots – are cooler regions on the photosphere.

Animation begins with sunspots at different latitudes lined up.

The sequence ends after one rotation of the equator.

The smallest of the loop prominences shown here is over three times bigger than the Earth (courtesy of National Solar Observatory/Sacramento Peak Observatory).

High resolution observations of the solar surface show a honeycomb pattern called granulation made of bright spots of convection 700 to 1000 kilometers across

Solar Atmosphere1.Chromosphere2.Corona

Chromosphere Color sphere 2000-3000 km thick Greek word chroma

(meaning color) Its temperature rises

outward away from the photosphere

Because it has a low density, you see emission lines of hydrogen (mostly at the red wavelength of 656.3 nanometers)

Cannot be seen by the naked eye because of the light from the photosphere

The edge of the chromosphere is made up of spicules

Spicule - a short-lived, relatively small radial jet of gas in the chromosphere or lower corona of the sun.

The thin chromosphere is visible in this solar eclipse

picture.

Corona is the luminous

“atmosphere” of the Sun extending millions of kilometers into space, most easily seen during a total solar eclipse

More details in the corona are seen when looking in the higher energy regions of the electromagnetic spectrum than visible light (extreme ultraviolet image from the SOHO spacecraft, courtesy of NASA and ESA).

The corona is known to be very hot because it has ions with many electrons removed from the atoms.

At high enough temperatures the atoms collide with each other with such energy to eject electrons (ionization)

Most of the corona is trapped close to Sun by loops of magnetic field lines. In X-rays, those regions appear bright. Some magnetic field lines do not loop back to the Sun and will appear dark in X-rays. These places are called ``coronal holes''.

Solar wind - Fast-moving ions can escape the Sun's gravitational attraction. Moving outward at hundreds of kilometers/second, these positive and negative charges travel to the farthest reaches of the solar system.

Aurorae – When the charged particles hit the planet's atmosphere, they make the gas particles in the atmosphere produce emission spectra.

STARS

Stars Each star in the sky

is an enormous glowing ball of gas

Star can live for billions of years

The composition of stars is studied using spectroscopy in which their visible light (the spectrum) is studied.

Spectroscopy is a technique in which the visible light that comes from objects is examined to determine the object's composition, temperature, motion, and density

Groups of StarsBinary star system Two stars that

are locked in elliptical orbit around their center of mass (their barycenter)

Clusters Larger group

of stars These are

relatively unorganized collections of stars

GLOBULAR CLUSTERA globular star cluster is a spherical group of up to a million stars held together by gravity.

These remote objects lie mostly around the

central bulge of spiral galaxies.

Stars are born in nebulae. Huge clouds of dust and gas collapse under gravitational forces, forming protostars.

THE BIRTH OF STARS

Stars are formed in nebulae, interstellar clouds of dust and gas (mostly hydrogen). Accretion Disk

The Eagle nebula, a stellar nursery illuminated by ultraviolet light which is emitted from the newborn stars.

The globule is cooled by emitting radio waves and infrared radiation (IR). It is compressed by gravitational forces and also by shock waves of pressure from supernova or the hot gas released from nearby bright stars.

A Central Core and a Protoplanetary Disk:

The central core becomes the star; the protoplanetary disk may eventually coalesce into orbiting planets, asteroids, etc.

Protostar:The contracting cloud heats up due to friction and forms a glowing protostar; this stage lasts for roughly 50 million years.

If there is not enough material in the protostar, one possible outcome is a brown dwarf.

A newborn starNASA captured images of a newborn star which looks EXACTLY like a Star Wars Light Saber

The protostar is now a stable main sequence star which will remain in this state for about 10 billion years. After that, the hydrogen fuel is depleted and the star begins to die.

Life span: The most massive stars

have the shortest lives. Stars that are 25-50

times that of the Sun live for only a few million years.

THE DEATH OF STARS

The core will run out of helium fuel

To maintain equilibrium it will contract and start to burn carbon

Eventually it will run out of fuel and collapse

The death cycle differs from how big the star is

When the core is just iron fushion ceases because iron is the most compact and stable of all the elements.

Stars like our Sun live for about 10 billion years.

Stars less massive than the Sun have even longer life spans.

Fate of a Star:

Black Dwarf Neutron Star

Black Hole

Sun-like Stars(Mass under 1.5 times the mass of the Sun) Red Giant Planetary Nebula White Dwarf Black Dwarf

Huge Stars(Mass between 1.5 – 3 times the mass of the Sun) Red SuperGiant Neutron Star

Giant Stars(Mass over 3 times the mass of the Sun) Red SuperGiant Supernova Black Hole

EVOLVED STAR-is an old star that is near the end of its existence. Its nuclear fuel is mostly gone. The star loses mass from its surface, producing a stellar wind. Older stars produce more stellar wind than younger stars.

Nuclear Fusion in Stars:

Nucleosynthesis

Why are stars hot and

bright???

Stars are giant nuclear reactors.

In the center of stars, atoms are taken apart by tremendous atomic collisions that alter the atomic structure and release an enormous amount of energy.

Nuclear Fusion- Is an atomic reaction

that fuels stars.- Stars are powered

by nuclear fusion in their cores, mostly converting hydrogen into helium.

The production of new elements via nuclear reactions

Small stars:• The smallest stars only

converts hyrodgen into helium

Medium-sized stars:• When the Hydrogen

becomes depleted, stars like our Sun can convert Helium into Oxygen and Carbon

Massive stars:• When their Hydrogen

becomes depleted, high mass stars convert helium atoms into carbon and oxygen, followed by the fusion of carbon and oxygen into Ne, Na, Mg, S, and Si.

Massive stars:• Later reactions transform

these elements into Ca, Ni, Cr, Cu, and others.

• When these old, large stars with depleted cores supernova, they create heavy elements

STAR TYPES

The SUN is a as a G2V type star, a yellow dwarf and main sequence star.

Hertzsprung - Russell Diagram The Hertzsprung -Russell (H-

R) Diagram is a graph that plots stars color (spectral type or surface temperature) vs. its luminosity (intrinsic brightness or absolute magnitude).

Most stars, including the sun, are “main sequence stars,” fueled by nuclear fusion converting hydrogen into helium

As stars begin to die, they become giants and supergiants.

Smaller stars (like our Sun) eventually become faint white dwarfs (hot, white, dim stars) that are below the main sequence.

SubtypesWithin each stellar type, stars are placed into subclasses (from 0-9) based on its position within the scale.

The Yerkes Luminosity Classes:By William Wilson Morgan and Philip Keenan)

Main Sequence Stars - Young Stars • Main sequence stars are

the central band of stars on the Hertzsprung-Russell Diagram.

Main Sequence Stars - Young Stars • These stars' energy

comes from nuclear fusion, as they convert Hydrogen to Helium.

Main Sequence Stars - Young Stars • Most stars (about 90%)

are Main Sequence Stars.

Main Sequence Stars - Young Stars • For these stars, the

hotter they are, the brighter they are. The sun is a typical Main Sequence star.

DWARF STARS• Dwarf stars are relatively

small stars, up to 20 times larger than our sun and up to 20,000 times brighter. Our sun is a dwarf star.

YELLOW STARS

• Yellow dwarfs are small, main sequence stars. The Sun is a yellow dwarf.

RED STARS• A red dwarf is a small, cool,

very faint, main sequence star whose surface temperature is under about 4,000 K. Red dwarfs are the most common type of star.

Proxima Centauri is a red dwarf.

Giant and Supergiant Stars

- Old, Large Stars

RED GIANT• A red giant is a relatively

old star whose diameter is about 100 times bigger than it was originally, and had become cooler (the surface temperature is under 6,500 K)

Betelgeuse is a red giant.

BLUE GIANT• A blue giant is a huge, very

hot, blue star. It is a post-main sequence star that burns helium.

SUPERGIANT• A supergiant is the largest

known type of star; some are almost as large as our entire solar system. These stars are rare. When supergiants die they supernova and become black holes.

Betelgeuse

SUPERGIANT

Rigel

Faint, Virtually Dead Stars:

WHITE DWARF• A white dwarf is a small,

very dense, hot star that is made mostly of carbon. These faint stars are what remains after a red giant star loses its outer layers.

BROWN DWARFA brown dwarf is a "star" whose mass is too small to have nuclear fusion occur at its core (the temperature and pressure at its core are insufficient for fusion). A brown dwarf is not very luminous.

NEUTRON STARA neutron star is a very small, super-dense star which is composed mostly of tightly-packed neutrons. It has a thin atmosphere of hydrogen. It has a diameter of about 5-10 miles (5-16 km) and a density of roughly 10 15 gm/cm3.

PULSARA pulsar is a rapidly spinning neutron star that emits energy in pulses.

Binary Stars

DOUBLE STARA double star is two stars that appear close to one another in the sky. Some are true binaries (two stars that revolve around one another); others just appear together from the Earth because they are both in the same line-of-sight.

BINARY STARA binary star is a system of two stars that rotate around a common center of mass (the barycenter). About half of all stars are in a group of at least two stars.

Polaris (the pole star of the Northern Hemisphere of Earth) is part of a binary star system.

ECLIPSING BINARYIs two close stars that appear to be a single star varying in brightness. The variation in brightness is due to the stars periodically obscuring or enhancing one another.

This binary star system is tilted (with respect ot us) so that its orbital plane is viewed from its edge.

X-RAY BINARY STARX-ray binary stars are a special type of binary star in which one of the stars is a collapsed object such as a white dwarf, neutron star, or black hole. As matter is stripped from the normal star, it falls into the collapsed star, producing X-rays.

X-RAY BINARY STAR

Variable Stars - Stars that Vary in Luminosity:

CEPHEID VARIABLE STARSCepheid variables are stars that regularly pulsate in size and change in brightness. As the star increases in size, its brightness decreases; then, the reverse occurs. Cepheid Variables may not be permanently variable;

The fluctuations may just be an unstable phase the star is going through. Polaris and Delta Cephei are examples of Cepheids.

MIRA VARIABLE STAR

A Mira variable star is a variable star whose brightness and size cycle over a very long time period, in the order of many months.

Miras are pulsating red giants that vary in magnitude as much as a factor of many hundred (by 6 or 8 magnitudes). Mira variables were named after the star Mira, whose variations were discovered in 1596.

BRIGHT STARS AND THE STARS CLOSEST

TO EARTHLuminosity - is the total brightness of a star or galaxy.

Apparent magnitude is a measure of the brightness of a celestial object as seen from Earth. The lower the number, the brighter the object. Negative numbers indicate extreme brightness.

Absolute magnitude is a measure of the inherent brightness of a celestial object. This scale is defined as the apparent magnitude a star would have if it were seen from a distance of 32.6 light-years (10 parsecs). The lower the number, the brighter the object. Negative numbers indicate extreme brightness.

SOME BRIGHT THAT CAN BE SEEN FROM

EARTH

(Alpha Scorpii) Antares (meaning "Rival of Mars") is the brightest star in Scorpius, one of the constellation in the zodiac.

ANTARES

(Alpha Boötis) Arcturus is the brightest star in the constellation Boötes (the herdsman). It is a red giant (spectral type K1.5IIIp) that is the fourth brightest star in the sky.

ARCTURUS

(pronounced "beetle juice") Betelgeuse (alpha Orionis) is the second-brightest star in the constellation Orion and one of the brightest stars in the sky.

BETELGEUSE

Deneb (which means "tail" in Arabic) is the brightest star in the constellation Cygnus (the swan); Deneb is also referred to as alpha Cygni, and is the tail of the swan.

DENEB

Polaris (alpha UMi) is the current pole star for the Northern Hemisphere; it is 1 degree from the exact Northern celestial pole. It is the larger star at the end of the handle of the Little Dipper (Ursa Minor). Polaris is also called the Lodestar or the Cynosure.

POLARIS

Orion, also known as "The Hunter," is a constellation in the zodiac. The brightest stars in Orion are Rigel, Betelgeuse, and Bellatrix. The Horsehead Nebula and the nebulae M42 and M43 are also in this constellation.

ORION

Rigel (beta Orionis) is the brightest star in the constellation Orion and one of the brightest stars in the sky. It is a blue (very hot) supergiant, over 60 million miles in diameter (almost 100 times bigger than the sun).

RIGEL

Sirius (meaning "scorching" in Greek), also known as the dog star, is the brightest star in the sky (except for the sun). It is in the constellation Canis Major (The Great Dog). Sirius is a main sequence star that is about 70 times more luminous than the sun.

SIRIUS

The closest star to us is the….

The Alpha Centauri system is in the star system that is closest to the Earth.

THE ALPHA CENTAURI SYSTEM

Proxima Centauri• The closest star to us. • also known as Alpha

Centauri C (because it is the dimmest star in the Alpha Centauri system).

The stars Alpha Centauri A and Alpha Centauri B are close binary stars.

Sirius (meaning "scorching" in Greek), also known as the dog star, is the brightest star in the sky (except for the sun). It is in the constellation Canis Major (The Great Dog). Sirius is a main sequence star that is about 70 times more luminous than the sun.

SIRIUS

NEBULAE

NEBULA• Is a huge, diffuse cloud of

gas and dust in intergalactic space.

• The gas in nebulae is mostly hydrogen gas (H2)

A stellar nursery is a nebula ( a large cloud of hydrogen gas in space) in which star formation is occurring (stars are formed from gas).

STELLAR NURSERY

These nebulae are frequently illuminated by ultraviolet light which is emitted from the newborn stars. One example of a stellar nursery is the Eagle nebula pictured above.

A planetary nebula is a nebula formed from by a shell of gas which was ejected from a certain kind of extremely hot star (a red giant or supergiant). As the giant star explodes, the core of the star is exposed. Planetary nebulae have nothing to do with planets.

PLANETARY NEBULA

Hourglass Nebula

The Hourglass

Nebula (NGC 6523) in M8

A nebula formed from by a shell of

gas

Eskimo NebulaThe Eskimo Nebula (NGC 2392) in Gemini was first sighted by William Herschel in 1787. The picture above is from the Hubble Space Telescope

An emission nebula is a nebula that glows (it emits light energy). The reddish light is produced when electrons and protons combine, forming hydrogen atoms.

EMISSION NEBULA

The free electrons combine with protons, forming hydrogen and red light. The Horsehead Nebula is in front of an emission nebula which illuminates the outline of the "horse head."

EMISSION NEBULA

A reflection nebula is a nebula that glows as the dust in it reflects the light of nearby stars. These nebulae are frequently bluish in color because blue light is more efficiently reflected than red light. A reflection nebula surrounds the Pleiades Cluster.

REFLECTION NEBULA

A ring nebula is a huge cloud of dust and gas that is shaped like a ring. Pictured to the right is M-57, a ring nebula in Lyra which is 2,000 light-years from Earth (this nebula was discovered by Ch. Messier).

RING NEBULA

Charles Messier

Ring Nebula

SOME WELL-KNOWN NEBULAE

The Crab Nebula (M1) is a cloud of intergalactic gas and dust. It is the remnant of a supernova that was seen on Earth in 1054. The Crab Nebula can be found in the constellation Taurus.

CRAB NEBULA

The Cygnus loop is a nebula, a supernova remnant in the constellation Cygnus. It covers a region in the sky six times the diameter of the full Moon. The nebula is almost spherical with some bright filaments.

CYGNUS LOOP

The Eagle Nebula (M16) consists of enormous columns of cool interstellar hydrogen gas and dust. This star-forming cloud (a stellar nursery) is illuminated by ultraviolet light that is emitted from newborn stars.

EAGLE NEBULA

The Horsehead Nebula is a huge cloud of dust in space that is shaped like a horse's head. It is luminous at its edges because it is in front of a bright emission nebula. It is located in the constellation Orion.

HORSEHEAD NEBULA

The Orion Nebula (M42 and M43) is a huge, nearby, turbulent gas cloud (mostly hydrogen) that is lit up by bright, young hot stars (including the asterism called Trapezium) that are developing within the nebula.

ORION NEBULA

Major Stars and Star Systems

CONSTELLATIONS

• A constellation is a group of stars that, when seen from Earth, form a pattern. The stars in the sky are divided into 88 constellations.

• The brightest constellation is Crux (the Southern Cross).

• The constellation with the greatest number of visible stars in it is Centaurus (the Centaur - with 101 stars).

• The largest constellation is Hydra (The Water Snake) which extends over 3.158% of the sky.

• There are also asterisms, smaller apparent star patterns within a constellation, like the Big Dipper (in Ursa Major), the Little Dipper (in Ursa Minor), Keystone (in Hercules), and the Pleiades (in Taurus).

THE 88 CONSTELLATIONS

CONSTELLATION FAMILY

• the Zodiac: 12 constellations are star groupings that lie along the ecliptic. There is actually a 13th constellation that crosses the ecliptic, Ophiuchus. The signs of the Zodiac are Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius.

• the Ursa Major Family: 10 constellations circling the northern celestial pole, including Ursa Major, Ursa Minor, Canes Venatici, Boötes, Coma Berenice, Corona Borealis, Camelopardalis, Lynx, Draco, and Leo Minor.

• the Perseus Family: 9 constellations depicting figures from the myth of Perseus, including Cassiopeia, Cepheus, Andromeda, Perseus, Pegasus, Cetus, Auriga, Lacerta, Triangulum.

The Hercules Family: 19 constellations depicting figures from the myth of Heracles, including Hercules, Sagitta, Aquila, Lyra, Cygnus, Vulpecula, Hydra, Sextans, Crater, Corvus, Ophiuchus, Serpens, Scutum, Centaurus, Lupus, Corona Australis, Ara, Triangulum Australe, Crux.

The Orion Family: 5 constellations, including Orion (the hunter), Canis Major and Canis Minor (Orion's two gods), Monoceros (the unicorn), Lepus (the hare).

The Heavenly Waters (aka the Cosmic Waters): 9 constellations whose names are related to water, including Delphinus, Columba, Equuleus, Vela, Puppis, Eridanus, Piscis Austrinus, Carina, Pyxis,

The La Caille Family: 13 Southern Hemisphere constellations, named by Nicolas Louis de Lacaille in 1756. Includes Norma, Fornax, Circinus, Telescopium, Microscopium, Sculptor, Caelum, Horologium, Antlia, Pictor, Reticulum, Octans, Mensa.

THE ZODIAC

The Zodiac is a family of constellations that lie along the ecliptic (the plane in which most of our Solar System lies). Usually, 12 constellations are listed in the Zodiac, but there is actually a thirteenth constellation that crosses the ecliptic, Ophiuchus (between Scorpio and Sagittarius).

WHY DO STARS TWINKLE?

Twinkle, twinkle, little star,How I wonder ...

• The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation).

• Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.

Stars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air).

• Stars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction.

• Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent).

• Stars would not appear to twinkle if we viewed them from outer space.

References:• http://

www.astronomynotes.com/starsun/s2.htm

• http://scied.ucar.edu/sun-regions

• http://www.enchantedlearning.com/subjects/astronomy/stars/index.shtml

THANK YOUGroup 5 – BEED 4A

God the Mother witnessed by the relationship between the sun, moon and stars.