Star Talk - Astronomy of Ursa Major

Remember the first constellation learned to recognize in the sky? I'll bet it was The Big Dipper, right? Those seven bright stars, two of which point the way to the North Star. Well, I have bad news. The Big Dipper isn't a constellation, at all! It's just a part of one...what we call an "asterism". Like the "teapot" in Sagittarius, or the "belt" of Orion. Asterisms can also be stars from several of the "official" constellations, like the Summer Triangle, consisting of three bright stars from three different constellations.

But, regardless of its technical classification, the Dipper is still the most well known star grouping in the sky. And it's part of Ursa Major - The Great Bear.

It's interesting that most cultures saw this shape as a bear. Native Americans, the ancient Greeks, the Germanic tribes of Europe, and others, all called it a bear. We don't know for sure what the Sumerians, who named most of the stars, saw, but they called this star "Dubhe", which means "bear" in Arabic. Dubhe, along with Merak, are the Pointers, which, as we all learned as kids, lead us to Polaris, the North Star. Polaris is the tail of Ursa Minor, the Lesser Bear, which resembles a smaller, dimmer dipper. (Try to say THAT three times!)

Ursa Major is interesting to astronomers because when we look in that direction, we are looking perpendicular to the plane of our galaxy...straight out the side window into deep space, with little to obstruct our view. The constellation Virgo is similarly placed, and together they form the realm of deep space objects...other galaxies, quasars, and the most distant objects we can detect. Many of these are known as Messier objects and bear M-numbers on charts. Those go back to an 18th century French astronomer, Charles Messier. Messier was a comet-hunter, and a contemporary of Edmund Halley, of Halley's comet fame.

The way you discover a comet is to scan the skies with a telescope, looking for anything that's fuzzy, and obviously not a star. When you find one, you go back to it in a few days to see if it's moved in relation to the background stars. If it has, and you are the first to report it, you have found a comet to bear your name. But more likely, it hasn't moved, and thus, isn't a comet.

Messier started compiling a personal list of these non-comet objects, which were just annoyances to him, so he wouldn't waste any time on them. He found 109 of them, and marked them on his star maps, designating them with numbers. He never did find a comet to make his name famous; and, in his eyes, he was a failure.

What he left us was a list that every astronomer uses regularly, and some of the most interesting sights in the universe. Messier's name and legacy are much more familiar to astronomers than almost any other, including Halley.

The area around Ursa Major claims 10 of the Messier objects and, with a little luck, you can spot most of them with binoculars. A small telescope will pick up all of them.

Happy hunting!