Jim (jazzmanjim) wrote, @ 2004-03-29 23:49:00

Neat Stuff in the Night Sky - Part 2
Just about everyone can find the Big Dipper (or the Plough, if you're in Britain) this time of year. It's likely the most recognizeable feature of the sky and the end of winter is a great time to see it and some of its notable neighbors.

The first neat fact about the Just about everyone can find the Big Dipper (or the Plough, if you're in Britain) this time of year. It's likely the most recognizeable feature of the sky and the end of winter is a great time to see it and some of its notable neighbors.

The first neat fact about the Big Dipper is that it's not a constellation of itself. The proper name for it is an "asterism" - a group of stars that make their own distinctive shape. You've probably seen other asterisms before: The Hyades (which makes up the horns of Taurus), Orion's Belt, and the Sword of Orion are perhaps the most notable. It's part of a constellation called Ursa Major or The Great Bear. Most folks, myself included would be hard pressed to identify the rest of the Great Bear, but that's okay. Most astronomers have a hard time finding it with the naked eye, too. It's not the easiest constallation to find, mostly because it's made up of relatively dim stars and because it's spread out over a good chunk of the sky.

There are a couple features about the Big Dipper I find interesting and to my knowledge they make it a truly unique bunch of stars. First, unlike many other constellations, the Big Dipper doesn't have any notable stars. They are all of the same approximate magnitude and none of them stand out to the point where they have memorable names. There aren't many constelations in the Northern Hemisphere for which this is true and certainly none as famous as the Big Dipper. Second, the Big Dipper has something called an "optical double". This is where two stars seem close enough to be thought to orbit each other, even though they don't. The optical double formed in the handle of the Big Dipper is the only one I can recall readily seen by the naked eye. To find this neat little sight, we have to find the Dipper first.

Look in the Northern Sky, slightly to the West. The Dipper will be hanging upside-down with the handle arcing gently to your right and the broad part of the dipper opening to the left. Once you've found that, the optical double is a snap to find. Look closely at the second star in the handle. If you don't have a lot of gorund light, and the weather's reasonably clear, you should see a small star right next to a brighter one.

From the Big Dipper, you can find four other constellations easily. We'll take the easiest one first - the one most folks learn as children. The back two stars of the Dipper (the ones which, right now will be the ones highest in the sky) are called the "pointer stars". Make a straight line betwen them then extend that line out from the bowl of the dipper to the first visible star. That star is Polaris, the North Star, the most visible star in Ursa Minor. It lies almost exactly on the North Magnetic Pole. It wasn't always the North Star, though. Because of a phenomenon known as precission, the north star shifts from one star to the next. This happens because the Earth doesn't rotate perfectly on its axis. There is a slight wobble that causes the north and south poles to slowly move in a cirle every 25,000 years or so which means that we won't have to worry about it for a while. :) Of all the stars which are likely to become "north stars" in the future, Polaris is the one closest to Magnetic North we'll ever know.

Let's go back to our pointer stars, and head in a line moving the other way. You'll come to a brightsh star named Regulus the most luminous star in the constellation Leo. Regulus means "heart of the lion", which makes sense to me considering it's smack in the middle of Leo. Oh, and there's another asterism here for you asterism collectors. Regulus is the bottom of what's called the "sickle of Leo" which you can find my moving up and following the curve of stars that form Leo's head.

Okay, let's go back to the Dipper. Do you notice how the stars of the handle make a gentle arc? Well, keep following that arc to Arcturus. Arcturus is the brightest star in Bootes the Herdsman. No, don't blame me for the name of these constellations. I would have named it "The Kite" because that's all I ever see when I look at Bootes. and I have no idea who Bootes is, either. I guess he was a famous herdsman who herded sheep really well and so, hey, a constellation. Arcturus is the fourth-brightest star in the sky and shines nearly as bright as Sirus over there in Canis Major (remember Canis Major?).

One more constellation and you can rest your next. Luckily, this one sits fairly low in the sky this time of year. Take that line you drew from the Dipper to Arcturus and make a beeline to Spica. Spica is the luminary of what may be the rarest thing nowadays, Virgo the...err..Virgin. Again, this constellation doens't look much like a virgin, but I assume that she was named by sailors out on a months-long voyage. I think we're lucky that all the constellations didn't get these kind of names. In the Southern Hemisphere, as a matter of fact, there's a wealth of nautically-named constellations (the Sextant, the Argo, the Compass, etc).

So there you go....five constellations for the price of one famous one!

Believe it or not, if you take these with the ones that group around Orion, you have most of the constellations in the sky during the early spring.

Enjoy!

	shyybabe 2004-03-30 12:31 (link)
	Thanks Jimmy. There's nothing in the world I'd rather do than converse with the stars. Thankfully, it's warming up enough that I can do it all night long. *smiles* (Reply to this) (Thread)