Thursday, August 13, 2015

Stargazing Journal: Light in August

The binary star Capella in the constellation Auriga.
Every year, the Perseid meteor shower falls roughly August 11-14: Earth returns to the trail of rocks left in space by Comet Swift-Tuttle, an extremely large and relatively fast comet, creating several nights of shooting stars that seem to flow out of the constellation Perseus. Delightfully for me, the Perseids begin on my birthday, giving me a kind of cosmic birthday present. It doesn't work out every year: clouds, full moons, and city lights can all interfere. But when the stars align (erm. Sorry), it makes for a beautiful night.

I watched last night and also early this morning; viewing is generally held to be best in the hour or two before dawn (which makes sense if you think about direction that the Earth rotates, I suppose). It was a perfect night here in west Michigan: cloudless, dry, a nearly new moon that was below the horizon all night anyway, and little enough light pollution to let the Milky Way emerge after your eyes adjusted to the dark. By 10:30, the Summer Triangle was high overhead, and you could actually see the Dolphin glowing faintly beneath Aquila. It's late enough in the summer that Arcturus and the Big Dipper had almost entirely sunk below the tree line around my parents' house—a sign I've come to associate with the advent of the school year. (The trees cover a good 25-30º of the sky above the horizon, though we are on a slight hill.) Even then, a few meteors were blazing across the sky. They don't last long—and they don't compete well with the glow of a city night—but they're hard to mistake.

But waking up at 5 this morning to catch the morning stars was extremely disorienting. I'm not normally up at that time, and I'm much more familiar with the summer sky than the autumn—so I had a hard time figuring out where everything was at first. (The sky at 5 a.m. this time of year roughly resembles what you'd expect of the autumn sky around midnight, to give you some idea of what I mean.) I don't know the autumn sky well, because I rarely watched stars as a kid on fall nights on account of school-year bedtimes and the chill—and Harvard Square wasn't a great place for darkness, even if I did get to use the Clay Telescope for nighttime lab sessions in my freshman year astronomy class.

So I cheated and used the Sky Guide app to get my bearings. It doesn't take all the fun out of the challenge (or vice versa): like any star chart, you have to work a little to align the chart with the sky, and the compass and gyroscope aren't 100% reliable. But I soon remembered so much: that Taurus was out (and with it, the Pleiades); Perseus (now high above), Andromeda, Cassiopeia, and Cepheus out re-enacting their myth; that even Orion, sign of autumn, is starting to rise, the star of its right shoulder (Bellatrix) poking above the trees. A steady trickle of meteors still flashed across the inky sky. The Summer Triangle had fled completely, well past the trees in the west, just a memory from hours earlier. I felt like I was looking into the future—getting a glance of October yet to come, my hands cold around a bowl of apple oatmeal. It may have been two years since I'd spotted the Pleiades. (How long will it be again now, with the stars drowned out by more city lights? Cities do cruel things to the starlight.)

This morning was the first time I've ever watched all the stars disappear from the sky. At 6, you could tell that astronomical twilight was starting—the eastern sky was softening to navy, threatening the faint stars just above. In twenty minutes, they nearly all disappear: dim Cepheus the first to fade, then the others. Cassiopeia, for being such a distinctive constellation, is surprisingly weak; it was gone with the indigo of the nautical twilight—and shortly after, most of the others. The Pleiades faded like sugar in a glass, with an inscrutable moment of dissolution; you blinked, and suddenly they were gone entirely. Only Capella and Aldebaran held on into the dawn, and I was surprised at how long they stayed—nearly till half past six, fifteen minutes till sunrise proper, well into the blue of the sky. Aldebaran went first, glowing rusty like a mote from an ember. Only then did Capella flicker out of sight. I was shocked to remember how bright it is. The approach of the Sun only made it seem even brighter, still strong as all the other feebler stars washed away. Capella is actually a binary star-system, yellow like the sun, but larger, and magnified to an intensity that carries much further than the sun's light could. And at 6:30, alone in the sky, they seemed to be boasting: you are no competition; you may be closer, but we are much stronger, brighter, grander than you are—like a king and queen on a double throne, calmer and more composed than the raving supergiants, but persistent, resilient, defiant even into the verge of the day.

*Bonus star trivia: The names of the stars in Orion's belt are Alnitak, Alnilam and Mintaka—all from Arabic, though only through corrupt transliteration into Western languages. Wikipedia, and my limited ability to make out the Arabic alphabet, says the traditional names in Arabic are النطاق an-niṭāq ("the girdle"), النظام an-niżām ("the pearls"), and منطقة manṭaqah ("the belt")

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