Stars

Stars...Galaxies= ...Universe

Stars

&nb= sp;

&= nbsp; Stars are made of different gases that are so dense that they act as a hot solid which gives off a continuous spectrum.&nbs= p; Stars are classified by how hot they are. The resulting order is OBAFGKM. Stars differ in many characteristi= cs including size, mass, color, temperature, and brightness.=

&nb= sp;

Class	Color	Surface temperature	Elements detected	Examples of stars
O	blue=	abov= e 30,000	He	10 L= acertae
B	blue= -white	10,0= 00-30,000	He H=	Rige= l, Spica
A	blue= -white	7,50= 0-10,000	H	Vega= , Sirus
F	yell= ow-white	6,00= 0-7,500	H-he= avier elements	Cana= pus, Procyon
G	yello= w	5,000= -6,000	Ca- o= ther metals	the s= un, Capella
K	oran= ge	3,50= 0-5,000	Ca-m= olecules	Arct= urus, Aldebaran
M	red<= o:p>	less= than 3,500	Mole= cules	Bete= lgeuse, Antares

&nb= sp;

Astronom= ers use light years to determine the distances to the stars. A light year is the distance that = light travels in one year. The spee= d of light is 300,000 km/s (3 x 10⁶ km/s). Light travels 9.5 trillion kilomet= ers in one year. The distance to the= North Star is 4,080,000,000,000,000 km. This is 431 light-years. Using par= allax and simple trigonometry, a scientist can find the distance to stars that are close to our planet Earth.

&nb= sp;

The rota= tion of the Earth gives the appearance that the sun and stars are in motion across = our sky. Stars are moving in spac= e, but their real motion is not easy to observe because stars are so far away.

&nb= sp;

Stars be= gin as a ball of gas and dust in space. Gravity pulls the gas and dust into a denser and denser sphere becom= ing hotter and hotter until the hydrogen in the center changes to helium through nuclear fusion. When this occ= urs, lots of energy is given off and a star is born. The cloud of dust and gas where st= ars form is called a nebula. When= a stars runs out of fuel, the core no longer releases energy and the center shrinks as the outer part expands. The star becomes a red giant or supergiant. All stars will become a red giant = or supergiant. What happens to a= star next depends on the mass of the star and they become a white dwarf, a neutr= on star, or a black hole.

&nb= sp;

Blue sta= rs: Blue stars quickly use up their hydrogen, expand, and become giants or

= supergiants.

&nb= sp;

White-dw= arf stars: White-dwarf stars are = small, hot stars left over from the centers of

= &nb= sp; old stars. They are ne= ar the end of their life. Our sun wi= ll become
= &nb= sp; a white-dwarf.

&nb= sp;

Red gian= t: The center of a star shrinks inwar= d and the outer parts expand outward

= when a stars runs out of hydrogen in the core. This happens to stars the

= size of our sun which is an average star. The atmosphere of the star will

= = grow very large and cool.

&nb= sp;

Supergia= nt: This is the same as the red giant = except the star is very massive and is

= called a supergiant.

&nb= sp;

Red-dwarf stars: Red dwarfs are stars w= ith low mass. The lowest mass sta= rs may be

= &nb= sp; of the oldest stars in the galaxy.

&nb= sp;

Supernov= as: Massive blue stars use up the hydr= ogen faster than other stars which

= &nb= sp; makes a lot of energy. This makes them very hot and blue. They do

= &nb= sp; not last as long as other stars and may explode in a great flash of light

= &nb= sp; that is called a super nova. The death of a large star by explosion is

= &nb= sp; called a super nova. T= he heavy elements of silver, gold, and lead are

= &nb= sp; formed by supernova explosions.

&nb= sp;

Neutron stars: When a supernova explo= des, the leftover materials at the center are

= &nb= sp; squeezed together to form a star about 20 kilometers in diameter. The

= particles in the star become neutrons. A neutron star is very dense.

= &nb= sp; One teaspoon of neutron star on Earth would weigh one billion metric=

= &nb= sp; tons.

&nb= sp;

Pulsars:= When a neutron star spins, it is c= alled a pulsar sending out radiation spinning

= rapidly. Radio telesco= pes detect this radiation as clicks or pulses.

&nb= sp;

Black holes: When the leftovers of a supernova are so massive, the leftovers collapse

= &nb= sp; and form a black hole. A black hole is an object of more than 3 solar

= &nb= sp; masses squeezed into a ball 10 kilometers across. The gravity of the

= &nb= sp; black hole is so strong that light cannot escape.

&nb= sp;

Galaxies

&nb= sp;

&= nbsp; Galaxies are large groups of stars held together by gravity. Galaxies are different sizes and shapes. Large galaxies have m= ore than a trillion stars. Small galaxies have a few million stars. Edwin Hobble in the 1920’s began the classification of galaxie= s.

&nb= sp;

Spiral galaxies: Spiral galaxies bul= ge in the center and have spiral arms. The spiral

= &nb= sp; arms consist of hot blue stars.&nbs= p; Cooler stars are at the center and

= &nb= sp; appear yellow. They seem to have a pinwheel shape. The Earth is<= o:p>

= &nb= sp; in a spiral galaxy. (Milky Way)

&nb= sp;

Elliptic= al galaxies: 33% of all galaxies= are massive amounts of stars that look like a

= &nb= sp; sphere or look elongated. The centers are very bright with little gas

= &nb= sp; or dust containing only old stars with no new stars forming. Some

= &nb= sp; are called giant elliptical galaxies and other are dwarf elliptical<= o:p>

= &nb= sp; galaxies. <= /span>

&nb= sp;

Irregular Galaxies: Galaxies that do no= t fit into any other group. Their s= hapes are

= &nb= sp; irregular. An example = is the Large Megellanic Cloud. =

&nb= sp;

Galaxies= contain billions of billions of stars along with gas clouds and star clusters. A nebula or nebulae are giant gas a= nd dust clouds. Gas clouds can be found in spiral galaxies. Elliptical galaxies do not have gas clouds. Globular clusters are groups of older stars that appear as a ball of stars containing 20,000 to 100,000 stars. They can be found in the halo of spiral galaxies such as our galaxy = or around giant elliptical galaxies. Open clusters are groups of stars usually along the spiral disk of a galaxy containing bright blue stars. They contain a few hundred to a few thousand stars.

&nb= sp;

Quasars are of the most powerful energy sources in the universe. They are very far away. They may be galaxies th= at ate forming. The quasar PKS 0637-752 has the power of 10 trillion suns and is 6 billion light years away. The= light you see left the quasar 6 billion years ago.

&nb= sp;

The Structure of the Universe<= /b>

&nb= sp;

Planets<= o:p>

        &= nbsp;   Solar Systems

        &= nbsp;           &nbs= p;   Star clusters to galaxies

        &= nbsp;           &nbs= p;            &= nbsp; Galaxy groups for Galaxy clusters

        &= nbsp;           &nbs= p;            &= nbsp;           &nbs= p; The Universe

&nb= sp;

&nb= sp;

&nb= sp;

&nb= sp;

The Big-Bang Theory

&nb= sp;

        &= nbsp;   The big-bang theory states that the universe began to expand with the explosion= of concentrated matter and energy and that the universe has been expanding ever since. According to the theor= y, the explosion took place 15 to 20 billion years ago shooting matter and energy = in all directions. The fastest traveling matter is farthest away.

&nb= sp;

&nb= sp;

&nb= sp;

&nb= sp;

&nb= sp;