Even the best astronomers can make mistakes. As an example, consider the great spiral galaxy M101, which is near the end of the Big Dipper's handle. The M stands for French astronomer Charles Messier, and the 101 means it was the 101st object in a catalog he compiled during the eighteenth century.
Most of Messier's objects are now known to be galaxies, star clusters, or big clouds of gas and dust known as nebulae. Messier's passion wasn't galaxies or nebulae, though -- it was comets. In fact, he discovered so many of the little iceballs that King Louis the Fifteenth of France called him the "ferret" of comets.
But galaxies and nebulae can look like comets, so they can fool comet hunters. So Messier decided to catalog all the objects masquerading as comets. He finished it in 1781, and it's a celestial "A list" of 103 objects.
M101, 102, and 103 are at the bottom of the list, but Messier didn't discover them. Instead, they were first spotted by a colleague, Pierre Mechain. Messier didn't have time to check them before his publishing deadline, but he included them anyway.
As it turns out, M101 and M103 both exist, but M102 doesn't. It might have been just a second glance at M101. So if you look at a modern version of Messier's catalog, you won't see anything under M102, except a note saying that it's a mistake. But given the enormous contributions of Messier and Mechain, it's probably a forgivable one.
More about M101 tomorrow.
Script by Ken Croswell, Copyright 2008
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