Hey, Sky Fans! Welcome back. January’s almost behind us already. It’s been a strange winter around where I live. Not a lot of snow, no, but it’s been stormy pretty much clear through since the middle of December. Lots and lots and lots of clouds and rain; plenty of wind. Ironically enough, as I type this, the skies are brightening and there’s more blue than not.
The other night, the last threads of another line moved out and left behind a good-sized stretch of open sky to the south. I happened to be outside and got chatting with a couple of neighbors who were walking their dogs. It was a nice break from the isolation of winter.
As we talked, we looked up, and stretched out in front of us was the constellation Orion, the sky’s brightest. It’s a lot of people’s favorite, and probably one of the two or three most recognizable. What other instantly recognizable ones can you think of? There’s Ursa Major, the Big Bear, which really isn’t recognizable as a bear at all. Instead, most of us here in the US see it as a giant and exciting spoon, Dipper Major, perhaps.
This brought up an interesting point, and brings us to this week’s word of the week: Asterism!
It’s a simple word, but a good one to know. An asterism is a group of stars that form some recognizable pattern in the sky. These stars can be in one or in more than one constellation. That brings up the question, “Wait… then, what’s a constellation?” Thanks for asking. A constellation is one of the 88 regions of the sky that are officially recognized by the International Astronomers’ Union (IAU). Constellations have borders and are adjacent to each other, covering the entire sky like countries or states cover continents. They’re used for mapping and navigating the sky.
“Hey, Laura, did you see the supernova in Libra?”
“No, Bill, thanks. I’ll have a look after lunch.”
Asterisms, on the other hand, are sort of the meat of everyday sky watching, the groups of stars that grab our attention when we head out at night and look up. In fact, asterisms are what we were all taught were constellations in grade school. The IAU’s definition superseded everyone else, intentionally or not. The current 88 constellations are based on the original asterisms people have been looking at for many thousands of years.
For example, the constellation Orion is much bigger than the seven or so stars that we recognize right away when we see it standing in front of us in the sky. How many of them can you name (I’ll put the answers below)? Those stars are an asterism. Also, Orion’s belt is an asterism within the main Orion asterism. The constellation Orion borders the constellations Gemini (the Twins), Taurus (the bull), Eridanus (the river), Monoceros (the unicorn) and Lepus (the cute and fuzzy astrobunny).
Back to the Big Dipper. It’s not a constellation, but an asterism within the constellation Ursa Major. The W-shaped patten in Cassiopeia; the Summer Triangle; the arcing-parenthesis-with-a-curvy-line-sticking-out-of-it-sort-of-thing in Scorpius.
While my neighbors and I were talking, I pointed what’s probably my favorite groups of stars of all, the Winter Circle. We’ve talked about it around here before, and we will again (bwuhahaha!!). It’s the glorious and enormous asterism of six or seven stars (I usually go with seven), that takes up pretty much the entire southern sky during the winter months.
Asterism is one of my favorite words. It’s an important word to have handy, a good one to have in your syntacto… lexi… wordpocket. It’s a good word to keep handy. It shows a certain different level of understanding about how modern astronomy operates, and also gives you some flexibility in how you see the sky. You can make up your own asterisms, as long as the pattern makes sense to you. I have a couple I like to think look like lamps to my eye, but how many lamps do we really need in the sky? Light pollution’s already a big enough problem. I also really like the fact that constellation comes from the Latin root for star, “stella” and asterism comes from the Greek root “aster.”
Okay, if you’re keeping track of the stars in Orion, the big seven are: Betelgeuse (left shoulder), Bellatrix (right shoulder), Saiph (left foot), Rigel (right foot), and the three belt stars from left to right Alnitak, Anilam, and Mintaka.
I hope to be back with a bit more tomorrow. Clear skies everyone!