Hey, sky fans. We’ve been talking a bunch about the comings and goings of the planets Jupiter, Saturn and Mars over the last couple of weeks. That’s not all there is this time of year, though. Sure, the planets are great, and all, don’t get me wrong, but now, mid-July, is the start of a great time to look away from those guys and check out the the stars a bit.
Do you remember a few months ago, when the Winter Circle was shining down on us? Well, now it’s summer’s turn. It’s a bit more of a mellow and subdued, though not any less great, asterism—one of those unofficial groups of stars that forms a recognizable pattern—but it’s summer, so subdued and mellow are the names of the game.
Here’s what you do the next time you’re out for an evening stroll or cannonball pageant. If you’re in the northern hemisphere, the skies are starting to darken a little earlier each day now as July moves on. To the east, by mid-evening, let’s say around 9:30 or 10:00, you’ll see a broad group of three bright stars. They’re widely set, so you might need to look for a second before it becomes clear to you. That’s the famous Summer Triangle. You got your self three points, three angles, and poof, a triangle. If you’ve got a fifth-grader handy, and please get their parents’ permission first, it’s not long before you learn it’s a scalene triangle. Isosceles to the left.
The lowest down of the three is Altair, the brightest star in Aquila the eagle, and the 12th brightest star in the whole nighttime sky. If you’re of a certain age, you’ll remember Altair from the title of one of those fun Choose You Own Adventure books we used to like. Altair is a little bigger than the Sun, is bright, and is one of the closest stars to us, too. It’s only about 16 light years away. So, the light we’re seeing now left it while everyone down here was panicking about the Y2K bug.
If you look to the left, just a little higher in the sky, you’ll see the blue-white supergiant Deneb (DEN-eb? Deb-EB? I’ve heard both; take your pick), the brightest star in Cygnus the swan. Deneb is an interesting star. In contrast to Altair, Deneb is positively huge, hundreds of times bigger than the Sun, and puts out many thousands of times more light. The reason it’s only 19th brightest is because it’s so far away—its light started on its way to your eye 2500 years ago—so its light has spread out and weakened. In fact, Deneb is one of the most luminous stars we know of, and you can see it in while standing outside swatting mosquitoes.
Higher up and between the two of them is Vega, the brightest star in Lyra the lyre, and the fifth brightest in the night sky. It’s more than twice the size of the Sun, and is 25 light years away. That’s far enough that its light left for Jack Rabbit Slim’s at almost the same time Vincent Vega and Mia Wallace did (a five-dollar milk shake?!). It’s much brighter than the other two Summer Triangle stars, big and bold, a truly gorgeous star even by itself.
These stars are all very bright, great to see, and easily found. They’ll be with us for a while, and will be gradually climbing higher in the skies, twisting toward the south each night until the start of September. Then, we’ll see them nearly due south at around this same time.
Let’s go back to Deneb and Altair for a second. Their side of the Summer Triangle lies right in the plane of our Milky Way. Imagine looking at the edge of a plate, no judgments. You’d see a thin line of porcelain in front of you. Our galaxy is a disk-shaped spiral, and we’re in that disk. So, we have a more or less edge-on view of our home galaxy, like we’re looking at the plate from within it. Those two stars are in the galactic plane, too, between us and the deep dustiness of the far off, downtown part of the galaxy, 20,000 light years away. That’s so far that the stars blend and blur together into a vague, bright haziness. It’s an incredible sight if the skies are right. If you follow that Debeb-to-Altair line further down toward the horizon, you’ll reach the constellation Sagittarius. Far behind it is the center of the galaxy. That’s when you get to start using exciting words like apogalacticon at rooftop parties.
I read a really sad statistic the other day. Apparently only about 15% of the entire world’s population live in a place where they can see the Milky Way. If you’re one of those people, please enjoy it. It’s time for us to start talking to the people in power to make some changes to cut down on light pollution. It’s a serious problems for nearly all of life, not just for people who can’t see the Milky Way.
Oh, speaking of the planets, August is going to be a heck of a month. We’ll talk more about that later on, but, for now, have a beer and a dog for me. I’m off to do some cannonballs! Clear skies, everyone!