Star Systems and Galaxies Multiple Star Systems Binary stars – star systems with two stars Eclipsing binary – system where one star periodically blocks light from another Star Clusters Open cluster – loose disorganized appearance and contains less than a few thousand stars Globular cluster – large grouping of older stars that is round and densely packed with stars, sometimes millions

Three types Spiral – bulge in the middle and arms that spiral out like a pinwheel an example is the Milky Way Elliptical – round or flattened balls Irregular – no shape, usually contain bright, young stars Galaxies – huge group of single stars, star systems, star clusters, dust, and gas bound by gravity

Additional Information Quasars – enormously bright object that looks like star many billion light years away Universe – all of space and everything in it Cosmic Background Radiation – mysterious glow that is thermal energy left over from the big bang – Dark Matter – matter that does not give off electromagnetic radiation – Dark Energy – mysterious new force causing the expansion of the universe to accelerate ***Most of the universe is made of dark matter and dark energy***