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STAR SYTEMS AND GALAXIES
• Our sun is a single star but most stars are members of groups of two
or more, called star systems.
• Two star systems are called binary. Three star systems are called
triple.
• Proxima Centauri is probably a triple. Alpha Centauri A and Alpha
Centauri B are part of a binary sytem.
• In a binary system usually one star is much brighter than the other.
• We can detect binary systems easily if one star blocks another,
called an eclipsing binary.
• We have found planets moving around stars in other systems. We
can only detect very large planets because the planets must have
enough gravity to effect the star.
Kruger 60: the binary pair are orbiting slowly around each
other. How long does a complete revolution take? Is the
movement clockwise or counter clockwise?
GALAXIES
• Our galaxy is called the Milky Way.
• Looks hazy to us beause the stars are so bright.
• There are three main kinds of galaxies, spiral, elliptical, and
irregular.
• Spiral galaxies have a pinwheel shape.
• They have arms that spiral outward.
• The Milky Way is a spiral galaxy. We cannot see the center
because it is hidden by stars and gases. It is 25,000 light years
away.
• Elliptical galaxies look like flattened balls. They contain little
dust and no new stars can form. Old stars only.
• Irregular galaxies have no shape. The Large Magellanic Cloud is
irregular and close to us (160,000 light years away)
•
(a)An artist’s concept of what the Milky Way would look like from another galax
(b)Looking into the center of our galaxy from earth (enhanced infrared)
Starburst galaxy. What kind of
galaxy is it?
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How do the stars in a galaxy
move?
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Sombrero GalaxyﾊThe Sombrero
Galaxy, a spiral system seen edge-on.
Spiral arms are not visible in this view.
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