The Universe, for all practice purposes, extends forever. But in every direction we look, as far deep into space as we can peer- we see galaxies. Astronomers have estimated that there are over 100 billion of them, but some suspect that there are, in fact, many, many more than that. They present themselves in all manner of shapes, sizes and orientations. For example, the spiral galaxy in this picture, which is 35 million light years from Earth, mostly presents its edge to us.

To better understand this perspective, take two CD's or DVD's out of their cases when you have a moment. Like these ubiquitous forms of entertainment and data storage, spiral galaxies also have a circular shape. Now, stack the two disks together and, to prevent scratches, arrange them so the printed label of each is the side that touches the other. Interestingly, the relative proportions between the thickness of the stacked disks to their diameter is surprisingly similar to many spiral galaxies, including the one in this picture. If you hold the two discs together at arm's length so that you only see their edge, then tilt their front down just a tad, you will have reproduced the view of the galaxy in this picture. As this exercise demonstrates, there is a lot about this galaxy that we cannot see.

However, if we could only see this galaxy face on then we would probably never realize things that are visible in this image. For example, notice that it is not flat. There's a slight curve, or warp, along its length. The warp may be caused by a small, yet unrecognized satellite galaxy, similar to the one visible toward the lower right in this wider view.

The gravity of each can distort the form of the other. Many large spirals have small, orbiting galaxies and often, the larger of the two is warped.

Also notice the faint partial ring that extends above and just below this galaxy. Its brightness has been exaggerated to make it more easily visible when, in fact, it is about one hundred times more dim than it appears here. It also may be partially responsible for the big spiral's warp.

Here's one more characteristic that CD's and DVD's share with spiral galaxies- they spin. But, while CD's and DVD's rotate at speeds approaching sixty revolutions per second, galaxies are so huge that they may take a few hundred million years to make one full turn around their center. In fact, many of the brightest stars that illuminate a galaxy radiate so much energy that they exhaust themselves and often explode before they complete one orbit around their galaxy's middle!