SkyCaramba weekly astronomy blog for the week ending October 1, 2011
The Andromeda Galaxy is both the biggest and farthest you can see with the naked eye. It’s 2.5 million light years away and 220,000 light years wide. Of course, a galaxy is a thing made up of things. Andromeda contains hundreds of millions of stars. We don’t know for sure, but it probably has its own planetary systems, comets, asteroids, and nebulae.
A thousand years ago, people didn’t have telescopes to point at the Andromeda Galaxy. It looked like a little cloud and was called that. In the 1700s and 1800s, astronomers were finding more such clouds with telescopes. In 1887, astrophotography had matured enough to capture images of spiral lines in the Andromeda Galaxy. Scientists first thought it was a solar system coming together. Some astronomers began to suspect that it was another galaxy and by 1925 they were convinced.
You can see the Andromeda Galaxy in a moderately dark sky. Find it by star hopping along and then above the constellation Andromeda on a September or October evening. A pair of binoculars will help. The galaxy will look like a fuzzy spot that just won’t come into focus. That’s the best view the first astronomers with telescopes could get, so you can understand why the galaxy was thought to be a cloud or nebula for so long.
If you look through a telescope, the lowest magnification you have will probably be the best. The galaxy is too big to fit in the view at bigger powers. It also gets harder to see when you spread its dim light among more of your retina. No matter how you view it, don’t expect to make out its spiral threads or individual stars any better than astronomers of 150 years ago. It will still look like a fuzzy patch of light.
The Andromeda Galaxy is heading our way. It and the Milky Way will collide in perhaps four billion years. It won’t be a collision like a meteor hitting a planet or two stars running into each other. Rather, most of the stars and other objects in the two galaxies will pass by each other. Over the course of hundreds of millions of years, each object will exert its gravitational pull on whatever else is near it and a new order will emerge.
We can’t know yet exactly what will happen, but it’s not unreasonable to think the Andromeda and the Milky Way will merge into a new galaxy. Maybe a few clusters of stars will be flung out. A few stars may collide. Whether there’s life on Earth then is something we can only imagine. The Andromeda Galaxy itself is now thought to have been formed from a collision or collisions of galaxies. Perhaps this has happened many times throughout the universe.
Another name for the Andromeda Galaxy is M31. It’s the 31st fuzzy object Charles Messier put on his famous list of things not to confuse with comets which often look like galaxies in telescopes.