The Cool, Clear Stars
We’re in a summer heat wave—the dog days of summer. When I was a kid, I always figured these were called the “dog days” because dogs looked like I felt; panting, beaten down, and generally miserable. Only later did I learn the phrase comes from astronomy: “dog” refers to Sirius, the dog star, so named for lying in the constellation of Canis Major, the big dog.
Or so I’m told. The association to Canis Major never made much sense. One problem is that Sirius isn’t visible at this time of year; it’s too close to the sun. Canis Major belongs to the winter group of the sky, constellations that you see on winter nights, because the sun is on the opposite side of the celestial sphere. By definition, the sun is up during the day; whichever stars the sun is near at that time of year are also up during the day, when you can’t see them. In the summer, Sirius is one of the stars made invisible by the glare of the sun. And why Sirius particularly? If medieval astronomers—who were often indistinguishable from astrologers—wanted to name this season for stars where the sun is, why not choose Gemini, Cancer, or Leo? Again, by definition, the zodiac consists of the twelve constellations in the ecliptic plane—the circle through which the sun seems to pass in the course of a year. These should be the crab days of summer, or the lion days a bit later.
Stars are on my mind because I’m brushing up on my stargazing. We’ll have an opportunity for real stargazing on our Arizona trip, and I want to be sure I have something to point out. This could be a challenge, given few distinguishing landmarks of the autumn sky and my own failing memory.
By accident of our position in the galaxy, prominent stars and constellations are relatively sparse in autumn. There is nothing like Orion or the Big Dipper, which everyone knows. Hercules and Pegasus in particular are nondescript squares, easily lost against the background. Pisces is an irregular loop and zig-zag. I used to know my constellations pretty well, thanks to a children’s astronomy program in my home town, but precisely because there’s more to see in winter than in autumn, our lessons began with the winter group and ended with the autumn group. Of course the last thing memorized is the one least well retained. So I have to study if I’m going to point anything out besides the north circumpolar group, the stars that are always visible at our latitude because they congregate around the north pole, fixed above the horizon.
Poring over star charts to relearn the celestial geography reminds me how different everything looks in the sky, in comparison to how it all looks on a map. Books—even large, unwieldy books—shrink everything to fit on the page. What looks like a dense, easily identified cluster on paper can be quite scattered when you go looking for the real thing. Shapes as well as sizes change; like maps, star charts distort the curved surface of the projected sphere of the heavens into a flat one. It can be hard to get your bearings. If you’re unlucky enough to lose one star behind a scrap of cloud, forget it. You can get similarly lost if you misidentify a planet as a star. Planets are relatively bright, and they move around, so they’re never seen on star charts, and misreading one is an easy mistake. Books eliminate a lot of background noise, minor stars that belong to no constellation’s construction. That’s no problem for Orion, but a big problem when looking for Pegasus, marked out by four dim stars barely distinguishable from their neighbors. Books indicate star brightness by the size of the spot; bigger spots for brighter stars. Trust me: t’s much harder to distinguish stars by brightness than ink spots by size. And, of course, the sky does not include bright connecting lines to mark out the constellations.
So preparation is a fair amount of work, but there are rewards. Away from the dimming blanket of city lights, the stars are quite beautiful, whether or not you know their names. Yes, even the autumn stars. Knowing the names makes you feel smart, and can impress your girl/boy-friend, especially a geek-chick like mine. If you can recall the mythology around the figures, telling the stories late into the night can be romantic. But best of all, at least in my imagination right now, is that we’ll be in the desert on an autumn evening, when it’s chilly enough to wear a jacket. God, I could use a chilly evening right about now.