The more we look at our place in the universe, the more we find how special it really is. For example, we are in a solar system that is a part of the spiral galaxy known as the Milky Way. Our place in the Milky Way is quite special, because we are essentially at the corotation distance from the center of the galaxy.1 This means we rotate around the center of the galaxy at the same rate as the spiral arms of stars that make up the galaxy. This produces a very stable environment for our planet, which is necessary in order for it to support life.
There are many, many other things we have learned about our solar system and the earth in particular that make it clear we are on a very special planet that orbits a very special star. If you are interested in learning more about how special our place in the universe is, I strongly recommend the book The Privileged Planet: How Our Place in the Cosmos is Designed for Discovery by Guillermo Gonzalez and Jay Wesley Richards. It details many discoveries in earth and space science that clearly show how special the earth and its solar system are. If even one of the many, many special factors that make life possible in our little corner of the universe were not present, you wouldn’t be around to be reading this blog post.
Even though we have known for a long time that the earth, the star we orbit, and our placement in the Milky Way galaxy are all quite special, we are just now beginning to find out that even the galaxy itself is special.
Thomas Dame and Patrick Thaddeus of the Harvard-Smithsonian center for Astrophysics have discovered what they think is an extension of the Scutum-Centaurus arm of the galaxy (see image above). Now as you might imagine, it is difficult to identify the different parts of a galaxy when you are observing it from the inside. Nevertheless, astronomers can develop models of what our galaxy might look like, and then they can compare those models to the observations that have been made. If you make enough observations, you can eventually winnow away most models until you have only one that is consistent with all observations. That model is pictured above.
Does this mean that the picture above is an accurate representation of the Milky Way? Not necessarily. However, it is the best we can do by making observations from the inside. Assuming the model is correct, there are two main arms in the Milky Way’s spiral – the Perseus arm and the Scutum-Centaurus arm. Until Dame and Thaddeus announced their discovery, it was thought that the Perseus arm was longer than the Scutum-Centaurus arm. However, if Dame and Thaddeus are correct, the two arms are essentially mirror images of one another.
What does this mean? Well, I think the Science News story that I read sums it up best:2
New finding suggests Milky Way has rare symmetry…A new study suggests the Milky Way doesn’t need a makeover: It’s already just about perfect.
So not only is our planet, the star it orbits, and its place in the galaxy special, the very galaxy of which it is a part is also special. It has a rare symmetry that makes it just about perfect.
Now, of course, if you want to force yourself to believe that our special planet that orbits a special star in a special part of a special galaxy is all a result of a bunch of happy coincidences, you are free to do so. However, I just don’t have that kind of faith. I prefer to follow the evidence, which tells me quite clearly that all this “specialness” is the result of careful planning and design.
1. DMishurov, Y.N. and L. A. Zenina, “Yes, the Sun is Located Near the Corotation Circle,” Astronomy & Astrophysics 341:81-85, 1999.
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2. Ron Cowen, “Galaxy Gets an Arm Extension,” Science News June 18, 2011, p. 14.
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