| MadSci Network: Astronomy |
Hi Gary. I am not sure I understand the question, but I will try to give the best answer I can. There are several things that need to be taken into account in order to answer this question. There are the distances to the galaxies relative to their sizes. Then there is the expansion of the universe that also will affect the answer. Next is the way light behaves as it travels through space. First, let's look at the expansion of the universe. At the Big Bang, the universe was concentrated in a small volume of space. As it expanded and cooled, matter began to clump together because of gravity into large-scale structures such as galaxies and clusters of galaxies. The universe has continued to expand throughout time and the distances have increased. I realize that this is oversimplified but the idea I am trying to get across is that these distance galaxies haven't always been distant and the light has always been radiating into space for us to see. Second, let's look at the closest galaxy to us. The Andromeda Galaxy is 2.2 million light years away from earth. It is comprised of trillions of stars and has a diameter of about 130000 light years. This gives us a ratio of about 17. Andromeda is 17 times farther away than it is wide. The distances to these objects are so much greater than their size that the distances to each side of the galaxy from earth is almost the same. Third, is the way that light behaves. On earth we are used to light traveling in a straight line. The distances here on earth are so small that this is the case. Over the vast distances in space from a distant galaxy, light will be affected by gravity and the path will not be a straight line but a curved one. This is most noticeable with a gravitational lens. Light coming from a distant galaxy will be bent around a nearer, massive object and create multiple images of the more distant object. The images can appear as arcs or as multiple galaxies. I have included several pages from The Astronomy Picture of the Day web site listed below. These are all examples of gravitational lenses. Astronomy Picture of the Day, June 1, 1999 Astronomy Picture of the Day, January 4, 1999 Astronomy Picture of the Day, March 30, 1998 Astronomy Picture of the Day, December 15, 1996 I hope that this answers your question.
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