Hey, sky fans! Here’s something fun for your Tuesday afternoon. Of the five brightest stars in the night sky, two, Canopus (second brightest), in the constellation Carina, and Rigil Kent, aka Alpha Centauri—the closest star system to us, in Centaurus (third) are southern stars, and are too far south to be seen from most places in the north. Even if you’re far enough south in the northern hemisphere for them to pop into your skies, neither gets above about 16 degrees above the horizon in the US, which is low and hard to see.
That’s right. Alpha Centauri is probably one of the most famous stars in the night sky, but since most people live in the northern hemisphere, most of the people have never seen it.
From there, as it turns out, at least one of the three other brightest stars is visible in the northern night sky every night of year. There’s some overlap, as every few months, one star hands the keys to the night to another, but one of them is always there. Sirius, in Canis Major, the brightest of them all gives way to Arcturus (fourth), in Böotes. in late April. Then, Vega, in Lyra (fifth) joins in for the warmer months. Round about the end of November, or early December, while Vega is low in the west in the evenings, Sirius comes back from its summer vacation and starts showing its face in the evenings’ eastern skies. These stars are very hard to miss and, together, make for sort of moveable asterism. It’s slow-moving change over course of the year, as the Earth makes its way around the Sun, and the night faces in different directions.
Arcturus, which is the brightest star in the entire northern half of the sky, is one of my favorite stars. Among other things, its name comes from the same root word that brings us Arctic (and, by extension, Antarctic). In ancient times, Arcturus was seen as the guardian of the bear—Ursa Major, which is in the northern sky. These days, by mid evening, it’s high overhead to the south, by far the brightest thing around, and passes its highest point in the sky, due south, just before 9:00pm around my centipede-filled estate. When the ice starts to melt, it’s one of the first stars I start to look for. At about 36 light years (LY) away, around 216,000,000,000,000 miles at 6 trillion miles to the LY, it’s pretty far. That’s so far that the kind people there are only now revving up for the Phillies’ and Royals’ trips to the World Series, and they’ll be shocked, really, when they learn about the triple spoilers of who Luke Skywalker’s father is, who shot J.R., and who killed the radio star. So, if you know of someone born in 1980, you can look up at Arcturus, and tell them that its light started its long trip across the incredible emptiness to their eye right around when they were born. These distances are all huge, though, and as it turns out, 36 LY makes it one of the closer stars to Earth. This partly explains why it’s so bright; its apparent magnitude: closer stars appear brighter than farther ones.
To find Arcturus, you can use the always-handy Big Dipper. Simply find it in the skies to the north, and then use the curve of its handle to “arc to Arcturus.” It’s the next bright thing you’ll hit once you jump off the end of the handle.
So, if you head out tonight, and find Arcturus using the arc method, you’re off to a good start. Tonight happens to be a terrific night for seeing the skies to the south. Arcturus will be high overhead, with the Moon nearly forming a straight line between it and Spica, the brightest star in Virgo. Crossing that line in sort of an inverted T shape will be Jupiter, to the right (westward), and Mars and Saturn to the left (eastward). It’ll be a gorgeous sight.
If you like, have a look at the two sketches above. One is of the skies to the south tonight at around 10:00pm near where I live. The other is of the Big Dipper and Arcturus. Try to get out there if you can, and clear skies, everyone!