International Dark Sky Week
Given the (usually) balmy weather in April during a week when moonlight won’t interfere, the International Dark Sky Association is encouraging everyone to step outside at night, look up, and enjoy the beauty of the sky. In some urban locales the effect of the coronavirus pandemic makes this even more apropos, since there has been a noticeable reduction of air pollutants being emitted, accompanied by a darkening of city lights as businesses shut down. While such impacts on Lyons are probably not that noticeable, the idea remains: Why not go outside anyway and take a look? You’ve been cooped up for weeks–what else have you got to do? Tell yourself now is the ideal time to learn some star names and identify a new constellation or two, just like you’ve always been promising yourself.
We’ll wait until 9:30 pm, when the sun has dipped to 18 degrees below the horizon, the official end of “astronomical twilight,” which means that all hints of twilight have vanished and the sky is as dark as it’s going to get. At this time you can glance off to the west and say goodbye to a few familiar old friends, like Orion the Hunter (which everyone recognizes, it seems) just stepping into the foothills (and in case you’re curious: no, ruddy Betelgeuse did not go supernova and has quite boringly recovered most of its brilliance). The brightest star in the night sky, Sirius, is about to dive into the southwestern horizon along with the rest of its constellation Canis Major, the Big Dog, while brilliant Venus still dominates the sky to the northwest.
But you knew all of those already, didn’t you? Time to learn something new!
Looking up and a little to the right of Venus, you’ll encounter the fourth-brightest star in the night sky visible from our latitude: Capella. It’s actually a quadruple star system, but dominated by a pair of yellow giants spinning around each other separated by less than the distance between the Earth and the sun. It forms one corner of a squashed hexagon shape that is supposed to be the constellation of Auriga the Charioteer, but actually looks more like a mangled cart from the movie Ben-Hur.
Look due west and halfway up from the horizon, and you’ll encounter a constellation that can almost looks like its namesake: Gemini, symbolizing the twin siblings Castor and Pollux. Currently the Twins are standing upright, with two faint parallel lines of stars dropping down toward the horizon symbolizing their bodies, while the heads of the pair are marked by prominent stars that bear their names.
Now turn and face due south, and tilt your head so far back it will feel like you’re looking straight up (although you’ll only be two-thirds of the way there). There you’ll find a mythical beast that almost looks like a real critter. Leo the Lion is lying down facing west, with his magnificent arched mane–less nobly described as a backwards question mark–as his most distinguishing feature. The dot at the bottom of the question mark is the bright star Regulus. Just like Capella, Regulus is also a quadruple star system, but instead shines with a blue-white light.
Now turn completely around to the north, and crane your head even further back. Passing almost straight overhead is what is arguably the most familiar and recognized asterism, or star pattern, of them all: the Big Dipper. It’s not really a constellation, but only the hindquarters and tail of the much larger Ursa Major, the Big Bear. Don’t bother trying to envision that bear, though. You would have to imagine the curved handle of the Dipper as a long tail–and whoever heard of a bear with a long bushy tail?
The two stars opposite the handle are well known as The Pointer Stars, in that they give you the line to look along in order to find Polaris, the North Star. When folks are asked, “which is the brightest star in the sky?” many will claim it to be Polaris. Which prompts the comeback, “well, if Polaris is the brightest, why the heck do we need a couple of fainter Pointer Stars to find it?”
The central star of the three forming the handle/tail of the Dipper/Bear has a fair degree of fame as well. It’s actually two closely spaced stars named Alcor and Mizar. They are said to have been used by the ancient Romans as an eyesight test: If you could distinguish the two, you could qualify to become a soldier in the Roman legion.
The curved handle also serves as a useful guide to locate our final two bright stars and constellations. Every fledgling astronomer learns to “follow the arc to Arcturus.” Let your eyes continue to trace the gentle curve of the handle eastward, and you’ll encounter the red giant star Arcturus, second only to Sirius in brightness. The star is a roughly solar-mass-sized star that shows what our sun is going to look like about 5 billion years from now. After depleting its hydrogen core, Arcturus has swollen to 25 times the sun’s diameter, and shines 170 times brighter. It forms a portion of Boötes the Herdsman, but don’t expect to see some old guy with a shepherd’s crook in the sky; instead, imagine a high-flying kite, with Arcturus at the tail where two streamers are attached.
Finally, from Arcturus you can “spin to Spica.” Continue following the gentle curve southward until you encounter the bright blue Spica in the constellation of Virgo. That star is pretty much the only one of any significance in the entire constellation. If you can manage to picture a young maiden lurking up there in the pattern, you’ve probably been standing outside by yourself for too long practicing social distancing. Time to call it an evening.
