Star Systems and GalaxiesStar Systems and Galaxies

Star Systems and GalaxiesStar Systems and Galaxieshazy band of light stretched across the sky hazy band of light stretched across the sky is the Milky Way, a spiral barred galaxy.is the Milky Way, a spiral barred galaxy.

It looks as if the Milky Way is very far It looks as if the Milky Way is very far away from Earth. Actually, though, Earth away from Earth. Actually, though, Earth is inside the Milky Way!is inside the Milky Way!

Star Systems and PlanetsStar Systems and Planets

Our solar system has Our solar system has only one star, the sun.only one star, the sun.

Half of all stars are Half of all stars are members of groups of members of groups of two stars called binary two stars called binary star systems.star systems.

In this star system you In this star system you would see two or more would see two or more suns in the sky.suns in the sky.

Double and Triple Star SystemsDouble and Triple Star Systems

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

Eclipsing BinariesEclipsing Binaries

A dim star in a binary star may pass in A dim star in a binary star may pass in front of a brighter star and eclipse it.front of a brighter star and eclipse it.

From Earth, the binary star would From Earth, the binary star would suddenly dimmer.suddenly dimmer.

A system in which one star periodically A system in which one star periodically blocks the light from another star is called blocks the light from another star is called an eclipsing binary.an eclipsing binary.

Planets Around Other StarsPlanets Around Other Stars

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

Gliese 581-NewEarth-like planet

Star ClustersStar ClustersMany stars belong to larger groupings Many stars belong to larger groupings called star clusters.called star clusters.

All the stars cluster form from the same All the stars cluster form from the same nebula at about the same time.nebula at about the same time.

There are two major types of star clusters: There are two major types of star clusters: open clusters and globular clusters.open clusters and globular clusters.

Star ClustersStar Clusters

Open clusters have a Open clusters have a loose, disorganized loose, disorganized appearance and appearance and contain no more than contain no more than a few thousand stars.a few thousand stars.

They often contain They often contain many bright many bright supergiants and supergiants and mostly gas and dust.mostly gas and dust.

Star ClustersStar Clusters

Globular clusters are Globular clusters are large groupings of large groupings of older stars.older stars.

Globular clusters are Globular clusters are round and densely round and densely packed with stars—packed with stars—some may contain some may contain more than a million more than a million stars.stars.

GalaxiesGalaxies

A galaxy is a huge groups of single stars, star A galaxy is a huge groups of single stars, star systems, star clusters, dust, and gas bound systems, star clusters, dust, and gas bound together by gravity.together by gravity.

There are billions of galaxies in the universe.There are billions of galaxies in the universe.

Astronomers have classified most galaxies into Astronomers have classified most galaxies into three main categories: spiral galaxies, elliptical three main categories: spiral galaxies, elliptical galaxies, and irregular galaxies.galaxies, and irregular galaxies.

Spiral GalaxiesSpiral Galaxies

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

Elliptical GalaxiesElliptical Galaxies

Not all galaxies have Not all galaxies have spiral arms.spiral arms.

Elliptical galaxies look Elliptical galaxies look like flattened balls.like flattened balls.

These galaxies These galaxies contain billions of contain billions of stars but have little stars but have little gas and dust between gas and dust between the stars.the stars.

Irregular GalaxiesIrregular Galaxies

Some galaxies do not Some galaxies do not have regular shapes. have regular shapes.

Because of this, they Because of this, they are known as are known as irregular galaxies.irregular galaxies.

Irregular galaxies are Irregular galaxies are typically smaller than typically smaller than other types of other types of galaxies.galaxies.

QuasarsQuasars

A quasar is an enormously bright, distant A quasar is an enormously bright, distant galaxy with a giant black hole at its center.galaxy with a giant black hole at its center.

Each of these black holes has a mass of a Each of these black holes has a mass of a billion times or more as great as the sun.billion times or more as great as the sun.

As enormous amounts of gas revolve As enormous amounts of gas revolve around the black hole, the gas heats up around the black hole, the gas heats up and shines brightly.and shines brightly.