Stars

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Stars
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What is a star?

• The objects that heat and light the planets in a
  system
• A star is a ball of plasma held together by its
  own gravity
• Nuclear reactions occur in stars (H ? He)
• Energy from the nuclear reactions is released as
  electromagnetic radiation

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Characteristics of Stars

• DISTANCE
• Measured in light-years
• The distance which a ray of light would travel in
  one year
• About 6,000,000,000,000 (6 trillion) miles
• 186,000 miles per second

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Characteristics of Stars

• Magnitude (brightness)
• A measure of brightness of celestial objects
• Smaller values represent brighter objects than
  larger values
• Apparent magnitude
• How bright a star appears to be from Earth
• Absolute magnitude (luminosity)
• How bright a star actually is

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Characteristics of Stars

• Temperature Color
• The color of a star indicates the T of the star
• Stars are classified by T
• Decreasing T (bright to dim)
• O, B, A, F, G, K, M Oh Be A Fine Girl, Kiss Me

http//www.seasky.org/cosmic/sky7a01.html
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Hertzsprung-Russell Diagram
http//www.dustbunny.com/afk/stars/lifecycle/hrdia
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Main Sequence Stars

• A major grouping of stars that forms a narrow
  band from the upper left to the lower right when
  plotted according to luminosity and surface
  temperature on the Hertzsprung-Russell diagram

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Types of StarsClassification
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http//www.answers.com/topic/stellar-classificatio
n
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Life Cycle of Stars
http//hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUB
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Life Cycle of Stars

• Begin their lives as clouds of dust and gas
  called nebulae
• Gravity may cause the nebula to contract
• Matter in the gas cloud will begin to condense
  into a dense region called a protostar
• The protostar continues to condense, it heats up.
  Eventually, it reaches a critical mass and
  nuclear fusion begins.
• Begins the main sequence phase of the star
• Most of its life is n this phase

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Life Cycle of Stars

• Life span of a star depends on its size.
• Very large, massive stars burn their fuel much
  faster than smaller stars
• Their main sequence may last only a few hundred
  thousand years
• Smaller stars will live on for billions of years
  because they burn their fuel much more slowly
• Eventually, the star's fuel will begin to run out.

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Life Cycle of Stars

• It will expand into what is known as a red giant
• Massive stars will become red supergiants
• This phase will last until the star exhausts its
  remaining fuel
• At this point the star will collapse

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Life Cycle of Stars

• Most average stars will blow away their outer
  atmospheres to form a planetary nebula
• Their cores will remain behind and burn as a
  white dwarf until they cool down
• What will be left is a dark ball of matter known
  as a black dwarf

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Life Cycle of Stars

• If the star is massive enough, the collapse will
  trigger a violent explosion known as a supernova
• If the remaining mass of the star is about 1.4
  times that of our Sun, the core is unable to
  support itself and it will collapse further to
  become a neutron star

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Life Cycle of Stars

• The matter inside the star will be compressed so
  tightly that its atoms are compacted into a dense
  shell of neutrons. If the remaining mass of the
  star is more than about three times that of the
  Sun, it will collapse so completely that it will
  literally disappear from the universe. What is
  left behind is an intense region of gravity
  called a black hole

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Life Cycle of Stars
http//www.seasky.org/cosmic/sky7a01.html