science project 3
TRANSCRIPT
A star is a massive, luminous ball of plasma that is held together by gravity. The nearest star
to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are
visible in the night sky, when they are not
outshone by the Sun.
Historically, the most prominent stars on the celestial sphere were
grouped together into constellations, and the brightest stars gained
proper names. Extensive
catalogues of stars have been assembled by astronomers, which provide standardized
star designations.
For most of its life, a star shines due to thermonuclear fusion in its core releasing energy that traverses the star's interior and then radiates into outer space. Almost all elements heavier than hydrogen and helium were created by fusion processes in stars. Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space.
The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history, including the diameter, rotation, movement and temperature. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russell diagram (H–R diagram), allows the age and evolutionary state of a star to be determined.
A star begins as a collapsing cloud of material composed
primarily of hydrogen, along with helium and trace amounts of
heavier elements. Once the stellar core is sufficiently dense, some of
the hydrogen is steadily converted into helium through the process of
nuclear fusion.The remainder of the star's interior carries energy
away from the core through a combination of radiative and
convective processes. The star's internal pressure prevents it from collapsing
further under its own gravity. Once the hydrogen fuel at the core is exhausted, those stars having at least 0.4 times the mass of the Sun expand to
become a red giant, in some cases fusing heavier elements at the core or in shells around
the core.
The star then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment, where it will form a new generation of stars with a higher proportion of heavy elements.
Binary and multi-star systems consist of two or more stars that are gravitationally bound, and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution.Stars can form part of a much larger gravitationally bound structure, such as a cluster or a galaxy.
Almost everything about a star is determined by its initial mass, including essential characteristics such as
luminosity and size, as well as the star's evolution, lifespan, and eventual fate.
AgeAge Most stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion years old—the observed age of the universe. The oldest star yet discovered, HE 1523-0901, is an estimated 13.2 billion years old. The more massive the star, the shorter its lifespan, primarily because massive stars have greater pressure on their cores, causing them to burn hydrogen more rapidly. The most massive stars last an average of about one million years, while stars of minimum mass (red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years.
Chemical compositionChemical composition
When stars form in the present Milky Way galaxy they are composed of about
71% hydrogen and 27% helium, as measured by mass, with a small fraction of heavier elements. Typically the portion of heavy elements is measured in terms
of the iron content of the stellar atmosphere, as iron is a common
element and its absorption lines are relatively easy to measure. Because the molecular clouds where stars form are steadily enriched by heavier elements
from supernovae explosions, a measurement of the chemical
composition of a star can be used to infer its age. The portion of heavier elements
may also be an indicator of the likelihood that the star has a planetary system.
The star with the lowest iron content ever measured is the
dwarf HE1327-2326, with only 1/200,000th the iron content
of the Sun. By contrast, the super-metal-rich star μ Leonis
has nearly double the abundance of iron as the Sun, while the planet-bearing star
14 Herculis has nearly triple the iron.There also exist
chemically peculiar stars that show unusual abundances of
certain elements in their spectrum; especially
chromium and rare earth elements.
DiameterDiameter
Due to their great distance from the Earth, all stars except
the Sun appear to the human eye as shining points in the night sky that twinkle because of the effect
of the Earth's atmosphere. The Sun is also a star, but it is close
enough to the Earth to appear as a disk instead, and to provide
daylight. Other than the Sun, the star with the largest apparent
size is R Doradus, with an angular diameter of only 0.057 arcseconds. The disks of most stars are much too small in
angular size to be observed with current ground-based optical
telescopes, and so interferometer telescopes are required in order to produce
images of these objects. Another technique for measuring the
angular size of stars is through occultation.
By precisely measuring the drop in brightness of a star as it is occulted by the Moon (or the rise in brightness when it reappears), the star's angular diameter can be computed.
Stars range in size from neutron stars, which vary
anywhere from 20 to 40 km in diameter, to supergiants
like Betelgeuse in the Orion constellation, which has
a diameter approximately 650 times larger than the Sun—about 0.9 billion kilometres.
However, Betelgeuse has a much lower density than the
Sun.
Betelgeuse is a red supergiant star approaching the end of its life
cycle
A white dwarf star in orbit around Sirius
The Sun is the nearest star to Earth The Pole star
A galaxy is a massive, gravitationally bound system that
consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but
poorly understood component tentatively dubbed dark matter. The
name is from the Greek root galaxias [γαλαξίας], meaning "milky," a
reference to the Milky Way galaxy. Typical galaxies range from dwarfs
with as few as ten million stars up to giants with one trillion stars,
all orbiting the galaxy's center of mass. Galaxies can
also contain many multiple star systems, star
clusters, and various interstellar clouds. The Sun is
one of the stars in the Milky Way galaxy; the
Solar System includes the Earth and all the other objects that
orbit the Sun.
Historically, galaxies have been categorized according to their apparent shape (usually
referred to as their visual morphology). A common form
is the elliptical galaxy,[5] which has an ellipse-shaped light
profile. Spiral galaxies are disk-shaped assemblages with
dusty, curving arms.
Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by
the gravitational pull of neighboring galaxies. Such interactions between
nearby galaxies, which may ultimately result in galaxies merging, may induce
episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to
as irregular galaxies.
There are probably more than 100 billion galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter.
The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.
Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center
of many, if not all, galaxies.
They are proposed to be the primary cause of active galactic nuclei found at the core of some
galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.
A spiral galaxy is shaped like a disk, usually with a bulge in the center and with arms that spiral outwards as the galaxy rotates. Spiral galaxies tend to contain more middle-aged stars along with clouds of gas and dust. Elliptical galaxies
contain older stars and very little gas and dust. They can be different shapes ranging from round,
to flattened, elongated spheres.
There are indeed different types of galaxies. The main types are spiral galaxies (like our own MilkyWay), elliptical galaxies and irregular galaxies. An irregular galaxy has an undefined shape and has lots of young
stars, dust and gas.
In colloquial usage, a constellation is what astronomers call an asterism: a group of
celestial bodies (usually stars) that appear to form a pattern in the sky or appear visibly related to each other.
Examples are Orion (which appears like a
human figure with a belt, often referred to as "The
Hunter"), Leo (which contains bright stars that
outline the form of a lion), Scorpius (which can seem
reminiscent of a scorpion), and Crux (a cross).
In astronomy, however, a constellation is an area of the sky, and contains all the stars
and other celestial objects within that area. The
International Astronomical Union (IAU)
divides the sky into 88 official constellations[1] with exact boundaries, so that every
direction or place in the sky is defined by one constellation.
Most of these constellations are centered on the traditional
constellations of Western culture. Constellations were devised by
ancient people to be able to recognize stars in the sky. The
shapes of constellations resemble objects familiar to those people.
Family Total Constellations
Ursa Major 10 Ursa Major, Ursa Minor, Draco, Canes Venatici, Boötes, Coma Berenices,
Corona Borealis, Camelopardalis, Lynx, Leo Minor
Zodiac 12 Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer
Perseus 09 Cassiopeia, Cepheus, Andromeda, Perseus, Pegasus, Cetus, Auriga, Lacerta, Triangulum
Hercules 19 Hercules, Sagitta, Aquila, Lyra, Cygnus, Vulpecula, Hydra, Sextans, Crater, Corvus, Ophiuchus, Serpens, Scutum, Centaurus, Lupus, Corona Australis, Ara,
Triangulum Australe, Crux
The Solar System consists of the Sun and those celestial objects bound to it by
gravity, all of which formed from the collapse of a giant molecular cloud
approximately 4.6 billion years ago. Of the retinue of objects that orbit the Sun, most
of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly-flat
disc called the ecliptic plane. The four smaller inner planets, Mercury, Venus,
Earth and Mars, also called the terrestrial planets, are primarily composed
of rock and metal.
Beyond Neptune's orbit lie trans-Neptunian objects composed mostly of ices
such as water, ammonia and methane. Within these regions, five individual objects, Ceres, Pluto,
Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own
gravity, and are thus termed dwarf planets. In addition to thousands of small bodies in those two
regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely
travel between regions.
The four outer planets, Jupiter, Saturn, Uranus and Neptune, also
called the gas giants, are composed largely of hydrogen
and helium and are far more massive than the terrestrials.
The Solar System is also home to two regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal.
The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar
medium known as the heliosphere, which extends out to the edge of the scattered disc. The hypothetical Oort cloud, which
acts as the source for long-period comets, may also exist at a distance roughly a
thousand times further than the heliosphere.
Six of the planets and three of the dwarf planets are orbited by natural satellites,[b] usually
termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of
dust and other particles.
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. Technically, the term natural satellite could refer to a planet orbiting a star, or a dwarf galaxy orbiting a major galaxy, but it is normally synonymous with moon and used to identify non-artificial satellites of planets, dwarf planets, and minor planets. As of September 2008, 335 bodies are formally classified as moons. They include 167 orbiting six of the eight planets, 6 orbiting three of the five dwarf planets, 104 asteroid moons, and 58 satellites of Trans-Neptunian objects, some of which will likely turn out to be dwarf planets. Some 150 additional small bodies were observed within Saturn's ring system, but they were not tracked long enough to establish orbits. Planets around other stars are likely to have natural satellites as well, although none have been observed.
The large gas giants have extensive systems of moons, including half a dozen comparable in size to Earth's moon: the four Galilean moons, Saturn's Titan, and
Neptune's Triton. Saturn has an additional six mid-sized moons massive enough to have achieved
hydrostatic equilibrium, and Uranus has five. Of the inner planets, Mercury and Venus have no moons at all; Earth has one large moon, known as the Moon; and Mars has
two tiny moons, Phobos and Deimos. It has been suggested that a few moons, notably Europa, one of
Jupiter's Galilean moons, may harbour life, though there is currently no direct evidence to support this claim.
Among the dwarf planets, Ceres has no moons (though many objects in the asteroid belt do). Pluto has three known satellites, the rather large Charon
and the smaller Nix and Hydra. Haumea has two moons, and Eris has one. The Pluto-Charon
system is unusual in that the center of mass lies in open space between the two, a characteristic of a
double planet system.
The first artificial satellite, The first artificial satellite, Sputnik 1, was , was launched by the Soviet Union in 1957. By 2009 launched by the Soviet Union in 1957. By 2009
thousands of satellites had been launched into orbit thousands of satellites had been launched into orbit around the Earth. These originate from more than around the Earth. These originate from more than 50 countries and have used the satellite launching 50 countries and have used the satellite launching capabilities of ten nations.capabilities of ten nations. A few hundred satellites A few hundred satellites
are currently operational, whereas thousands of are currently operational, whereas thousands of unused satellites and satellite fragments orbit the unused satellites and satellite fragments orbit the Earth as Earth as space debris. A few . A few space probes have have been placed into orbit around other bodies and been placed into orbit around other bodies and become artificial satellites to the Moon, Venus, become artificial satellites to the Moon, Venus,
Mars, Jupiter and Saturn.Mars, Jupiter and Saturn.
In the context of In the context of spaceflight, a , a satellitesatellite is an is an object which has been which has been placed into placed into orbit by by human endeavor. endeavor.
Such objects are sometimes called Such objects are sometimes called artificial satellitesartificial satellites to distinguish them to distinguish them from from natural satellites such as the such as the Moon..
Satellites are used for a large number of purposes. Common types include military
(spy) and civilian Earth observation satellites, communication satellites,
navigation satellites, weather satellites, and research satellites. Space stations and
human spacecraft in orbit are also satellites. Satellite orbits vary greatly,
depending on the purpose of the satellite, and are classified in a number of ways.
Well-known (overlapping) classes include low Earth orbit, polar orbit, and
geostationary orbit.Satellites are usually semi-
independent computer controlled systems. Satellite subsystems attend
many tasks, such as power generation, thermal control, telemetry,
attitude control and orbit control.
• National Aeronautics And Space Administration (NASA)• American Institute for Astronautics and Aeronautics• Space.com• Smithsonian Air & Space• National Space Society (NSS)• Space Frontier Foundation (SFF)• Space Studies Institute (SSI)• Planetary Society• Mars Society• TsNIIMash• Island One Society• European Space Agency• Italian Space Agency• National Space Development Agency of Japan (NASDA) • British National Space Centre (BNSC) • FAA - Commercial Space Transportation • National Oceanic & Atmospheric Administration (NOAA)• European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)• The Austrian Space Agency• Space Research Organization Netherlands (SRON)• Norwegian Space Centre
• Committee on the Peaceful Uses of Outer Space (COPUOS)• Indian Space Research Organisation (ISRO) • Russian Aviation and Space Agency (RSA)
• French Space Agency - Centre National d'Etudes Spatiales (CNES) • Brazilian National Institute for Space Research (INPE)
• Cooperative Research Centre for Satellite Systems (CRCSS)• Swiss Space Office (SSO)
• Indian National Remote Sensing Agency (NRSA)• The Polish Space Research Centre
• China National Space Administration (CNSA)• Swedish National Space Board (SNSB)
• Asia-Pacific Satellite Communications Council (APSCC)• Spanish Centre for the Development of Industrial Technology
(CDTI) • Argentine Association for Space Technology
• Space Enterprise Council• Finnish National Technology Agency (TEKES)• German National Aerospace Agency (DLR)
• Canadian Space Agency (CSA)
• Space Research Organization Netherlands (SRON)• Norwegian Space Centre
• Committee on the Peaceful Uses of Outer Space (COPUOS)• Indian Space Research Organisation (ISRO) • Russian Aviation and Space Agency (RSA)
• French Space Agency - Centre National d'Etudes Spatiales (CNES) • Brazilian National Institute for Space Research (INPE)
• Cooperative Research Centre for Satellite Systems (CRCSS)• Swiss Space Office (SSO)
• Indian National Remote Sensing Agency (NRSA)• The Polish Space Research Centre
• China National Space Administration (CNSA)• Swedish National Space Board (SNSB)
• Asia-Pacific Satellite Communications Council (APSCC)• Spanish Centre for the Development of Industrial Technology (CDTI)
• Argentine Association for Space Technology • Space Enterprise Council
• Finnish National Technology Agency (TEKES)• German National Aerospace Agency (DLR)
• Canadian Space Agency (CSA)
