Spiral Galaxies

The most beautiful type of galaxies are Spiral Galaxies. Spiral galaxies are galaxies with a central, dense area and spiraling arms which are often sites of star formation. These common galaxies have two major parts: a central, flat disk containing a dense cloud of interstellar matter and young star clusters (mostly on the arms) and a central bulge (or nucleus) containing older stars

So where do the spirals come from? Like ripples in a pond, the spiral arms seen in this kind of galaxy are circling waves. These waves cause new stars to form. That's right, they are like star farmers, planting star seeds where ever they go.
Some of the new stars created in the wave are very large. Because of their size these large stars glow brighter than their smaller cousins, causing the nearby dust clouds to glow brightly. Thus any area near one of these waves glows like a fluorescent light.

In other words you can't actually see the waves, the spirals that we see are the glowing clouds illuminated by large, hot stars. As the waves move on the clouds behind them dim down, no longer glowing until another wave passes through.

The large bright stars created in the waves don't live very long. Their large size makes them burn all their fuel quickly. Usually they die before they ever leave the wave. Only the smaller stars which do not glow brightly survive to leave the waves they formed in.
The Milky Way and the Andromeda Galaxy (M31) are two of a multitude of known spiral galaxies. The Milky Way Galaxy is a spiral galaxy; our sun and solar system are a small part of it. Most of the stars that we can see are in the Milky Way Galaxy. The main plane of the Milky Way looks like a faint band of white in the night sky. The Milky Way is about 100,000 light-years in diameter and 1,000 light-years thick. This spiral galaxy formed about 14 billion years ago. It takes the sun roughly 250 million years to orbit once around the Milky Way. The Earth is about 26,000 light-years from the center of the Milky Way Galaxy. The center of the Milky Way galaxy is towards the constellation Sagittarius. The Local Arm is the arm of the Milky Way Galaxy where our solar system is located. It is also called the Orion Arm.

The Andromeda Galaxy (also known as M31) is the closest major galaxy. It is a spiral galaxy (like our galaxy) and is in the Local Group. It is flanked by two dwarf elliptical companion galaxies (M32 and M110). It is part of the Local Group, a cluster of galaxies to which we (in the Milky Way) belong. The Andromeda Galaxy can just be seen with the naked eye in the constellation Andromeda. Andromeda is the farthest object that can be seen with the naked eye. It is about 2,400,000 light-years from Earth. It is 150,000 light-years wide. Recently, the Hubble Space Telescope found that Andromeda has a double nucleus. This second nucleus is probably from an ancient collision with a smaller galaxy.

The Andromeda Galaxy