Star+Notes

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l How are stars classified?
=__STARS__=

Star Classification
=//__Sun Stats__//=

l //__Composition__//è 70.89% (H) 27.43% (He) 1% other
=//__Star Classification__//=

§ O and B stars are uncommon but very bright; M stars are common but dim..
=//__Visible Spectra__//=

3) a hot compressed gas
=**//__Dark Line Spectrum__//**=

l Dark line spectrum is also known as the absorption spectrum.
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l What is a dark line spectra?
=__Temperature measurement__=

l The Doppler-broadened line to be used to measure the temperature of the emitting gas.
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l Which stars are the coolest?
=__Hertzsprung - Russell Diagram__=

l On it, astronomers plot stars' color, temperature, luminosity, spectral type, and evolutionary stage. This diagram shows that there are 3 very different types of stars:
=//__H-R Diagram__//= =**//__Main Sequence Stars__//**=
 * See the class web site www.nahsess.wikispaces.com

l For these stars, the hotter they are, the brighter. These stars are in the most stable part of their existence; this stage generally lasts for about 5-10 billion years.
=//__Life of a Star__//=

l Then become neutron stars, or black holes (again depending on their mass).
=//__Life of a Star__//=

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=Types of Stars=

==l //__RED DWARF__// 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== ==l //__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). They are frequently orange in color.==

==l __SUPERGIANT__ A supergiant is the largest known type of star; some are almost as large as our entire solar system. Betelgeuse is a redsupergiant. It is about 20 times as massive as the Sun about 14,000 times brighter than the Sun, and about 600 light-years from Earth.==

l These stars are rare. When supergiants die they supernova and become black holes.
=Faint, Virtually Dead Stars:=

l **//__WHITE DWARF__//**
==l **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. Their nuclear cores are depleted. They are about the size of the Earth (but tremendously heavier)!**==

__NEUTRON STAR__
==l A 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 and a density of roughly 10-15 gm/cm3.==

l //__PULSAR__// A pulsar is a rapidly spinning neutron star that emits energy in pulses.
=//__Binary Stars__//:= ==l //__DOUBLE STAR__// A double star is two stars that appear close to one another in the sky. Some are true binaries others just appear together from the Earth because they are both in the same line-of-sight.==