Star Systems and Galaxies

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Star Systems and Galaxies
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Star Systems and Galaxies

• hazy band of light stretched across the sky is
  the Milky Way, a spiral barred galaxy.
• It looks as if the Milky Way is very far away
  from Earth. Actually, though, Earth is inside
  the Milky Way!

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Star Systems and Planets

• Our solar system has only one star, the sun.
• Half of all stars are members of groups of two
  stars called binary star systems.
• In this star system you would see two or more
  suns in the sky.

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Double and Triple Star Systems

• The prefix bi means two. What does Tri mean?
• An example of a binary star system is in the
  handle of the Big Dipper.
• Those with three stars are called triple stars.
• An example of a triple star system is that of
  Alpha Centari.
• Alpha Centari is the closest star to ours, but it
  is really three stars.

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Eclipsing Binaries

• A dim star in a binary star may pass in front of
  a brighter star and eclipse it.
• From Earth, the binary star would suddenly
  dimmer.
• A system in which one star periodically blocks
  the light from another star is called an
  eclipsing binary.

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Planets Around Other Stars

• Triple star system, astronomers found a world
  called HD 188753 Ab.
• We could not set foot on this planet though,
  since its a gas giant, roughly the mass of
  Jupiter, orbiting its parent star every 3.3 days!

Gliese 581-New Earth-like planet
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Star Clusters

• Many stars belong to larger groupings called star
  clusters.
• All the stars cluster form from the same nebula
  at about the same time.
• There are two major types of star clusters open
  clusters and globular clusters.

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Star Clusters

• Open clusters have a loose, disorganized
  appearance and contain no more than a few
  thousand stars.
• They often contain many bright supergiants and
  mostly gas and dust.

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Star Clusters

• Globular clusters are large groupings of older
  stars.
• Globular clusters are round and densely packed
  with starssome may contain more than a million
  stars.

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Galaxies

• A galaxy is a huge groups of single stars, star
  systems, star clusters, dust, and gas bound
  together by gravity.
• There are billions of galaxies in the universe.
• Astronomers have classified most galaxies into
  three main categories spiral galaxies,
  elliptical galaxies, and irregular galaxies.

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Spiral Galaxies

• Spiral galaxies are galaxies that have the shape
  of twin spirals.
• Our galaxy has the same spiral, pinwheel shape.
• The spiral arms contain many bright, young stars
  as well as gas and dust.

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Elliptical Galaxies

• Not all galaxies have spiral arms.
• Elliptical galaxies look like flattened balls.
• These galaxies contain billions of stars but have
  little gas and dust between the stars.

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Irregular Galaxies

• Some galaxies do not have regular shapes.
• Because of this, they are known as irregular
  galaxies.
• Irregular galaxies are typically smaller than
  other types of galaxies.

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Quasars

• A quasar is an enormously bright, distant galaxy
  with a giant black hole at its center.
• Each of these black holes has a mass of a billion
  times or more as great as the sun.
• As enormous amounts of gas revolve around the
  black hole, the gas heats up and shines brightly.