http://seds.lpl.arizona.edu/messier/more/mw_sky.html The Milky Way is the home of our Solar System along with at least 200 billion other stars and planets. It contains thousands of clusters and nebulas. It is the home of nearly all the objects of Messier’s catalog that aren’t their own galaxies. The mass of our giant galaxy is somewhere between 750 billion and one trillion solar masses. The diameter is estimated to be about 100,000 light years. The galaxy has three main components: a disk, in which the solar system resides, a central bulge at the core and an all encompassing halo. The disk of our galaxy exhibits it’s spiral structure and is part of the prominent nuclear region which is part of a notable bulge/halo component. http://www.damtp.cam.ac.uk/user/gr/public/gal_milky.html The Milky Way is categorized as a Hubble type Sb or Sc spiral. It is unclear if the galaxy has a bar in its spiral so that is why its classification is unsure. The image above is that of the spiral galaxy M83, which is thought to be similar in size and shape to our Milky Way, causing some to classify our galaxy as a Abbc type spiral. The bright ban of light seen at night, is usually what is referred to as the Milky Way. The bright plane is actually the disk of our galaxy. The disk is composed of mostly Population 1 stars, which are blue and fairly young, which range between a million and ten billion years old. The disk of our galaxy has four spiral arms, which contain interstellar matter, diffuse nebulae, and young stars and open star clusters emerging from that matter. The spiral arms are also where the active star formations take place. The arms are approximately 300 pc thick and 30 kpc in diameter. The red stars, or the older stars, in our galaxy are located in the bulge component, which is the center of our galaxy. These Population II stars are thought to be 10 billion years old. The bulge component also contains the...
