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Diagram a comet
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http//media.nasaexplores.com/lessons/01-072/image
s/cometdiag.gif
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Describe GALAXY
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• A galaxy contains stars, gas, and dust which are
  held together as a group by gravity. There may be
  millions, or even billions, of stars in one
  galaxy. There are billions of galaxies in the
  universe.

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How are galaxies classified?
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Galaxies are classified according to their shape.
Some galaxies are called "spiral", because they
look like giant pinwheels in the sky. The galaxy
we live in, the Milky Way, is a spiral galaxy.
Some galaxies are called elliptical", because
they look like flat balls. A galaxy may be called
"irregular" if it doesn't really have a shape. A
new type of galaxy was discovered recently,
called a "starburst" galaxy. In this type of
galaxy, new stars just seem to 'burst out' very
quickly. http//starchild.gsfc.nasa.gov/docs/Sta
rChild/universe_level1/galaxies.html
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Describe STAR
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• A star is a brilliantly glowing sphere of hot gas
  whose energy is produced by an internal nuclear
  fusion process. Stars are contained in galaxies.
• http//starchild.gsfc.nasa.gov/docs/StarChild/univ
  erse_level2/stars.html

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What is the Hertzsprung-Russell Diagram?
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• A tool that shows relationships and differences
  between stars. It shows stars of different ages
  and in different stages

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Diagram the life cycle of a star
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www.seasky.org/cosmic/sky7a01.html
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Describe the types of stars
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• Main Sequence Stars - maintains a stable nuclear
  reaction.
• Red Giants - a large star that is reddish or
  orange in color. It represents the late phase of
  development in a star's life, when its supply
  hydrogen has been exhausted and helium is being
  fused
• White Dwarfs - the remnant of an average-sized
  star that has passed through the red giant stage
  of its life. After the star has used up its
  remaining fuel.