“OUR GALAXY” Definition of a Galaxy: a huge group of individual stars, star clusters, dust, and gas bound together by gravity.

“Our Galaxy” is an Example of a SPIRAL GALAXY * Has an estimated billion stars *Milky Way has a diameter of more than 100,000 light years *The spiral arms of Gas, Dust, and YOUNG STARS wind through the galaxy’s disk

Our Solar System lies in the Milky Way’s disk Within a Spiral Arm about 2/3 from the Center The Center of this galaxy is a Bulge of stars surrounded by an Immense Halo of globular clusters.

As we look at edge of the galaxy from Earth, it appears as a band in the night sky (instead of a spiral)  Flattened Disk Shape is caused by its rotation.  The sun takes about 220 million years to complete ONE orbit around the Galaxy’s Center

 Are Enormously Bright Centers of Distant Young Galaxies  Produce More light than hundreds of galaxies the Size of the Milky Way  Matter spiraling into a Super Massive Black Hole with the Mass of a Billion Stars!  The gravitational energy of this matter is transformed into Electromagnetic Radiation.

Barred Spiral Galaxy

Elliptical Galaxy Spiral Galaxy Irregular Galaxy

 ConstellationAlso:  Star system Eclipsing Binary  Binary star  Globular cluster  Galaxy  Spiral galaxies  Barred-spiral galaxies  Elliptical galaxies  Irregular galaxies  Quasars

 Open Cluster  Associations  Bright,young stars  Fornax cluster  Edwin Hubble  Old Stars  Spiral Shape  M 87 (example of a galaxy type)  Magellanic Cloud (example of a galaxy type)  Milky Way  Big Bang  Red shift  13.7 Billion years old