SCIE 1920U Chapter 11: 11 Galaxies
Document Summary
Milky way galaxy looks like a band of light crossing the sky. The name milky way comes from the appearance of this band, which looked to ancient people like a ribbon of flowing milk. Spiral galaxy has arms on a face on view. From the side, the spiral arms blend into a thin disk that contains more than 100 billion stars. At the center of the disk, we find a bright central bulge. Surrounding the disk is a vast, roughly spherical halo. The disk is about 100,000 light-years in diameter, but only about 1000 light years thick. We are half way from the center and end half from the edge. The galactic disk is filled with interstellar gas and dust known collectively as the interstellar medium that obscures our view when we try to peer directly through it. Stars in the disk orbit in roughly circular paths that all go in the same direction in nearly the same plane.
