Galaxies

Galaxy

*  A collection of stars, nebulae,  gases, dust and planets

            *  Objects in a galaxy are held together

            as a unit by gravity

            *  There are at least 50 billion galaxies

Types of Galaxies

            *  Classified into 4 groups based on shape

                        *  galaxies vary in size in each group

                        *  a galaxy contains billions of stars

            *  Groups

                        *  elliptical, spiral, irregular, barred

                        spiral

Elliptical Galaxies

*  Shaped like a football or flattened sphere

*  Most do not rotate, but a few rotate very slowly

*  Contain less dust and gas than spiral

*  Largest are made of trillions of stars

Spiral Galaxies

            *  Shaped like a flat disk with a bulge in

            the center; have long spiral arms from

            the center

*  Arms rotate from the center like a pinwheel

            *  Contain large amounts of gas and dust

            * Our galaxy, the Milky Way, is one

Irregular Galaxies

            *  Don't have a regular shape

            *  Vary greatly in size

            *  Least common type of galaxy

Barred Spiral Galaxy

*  Arms are attached to a straight bar shape instead of center

*  Bar is usually much brighter and denser than the arms

*  Less common than spiral galaxies