It’s time for the Perseids again! This has to be the most fun shower of the year. The sky is often clear, weather pleasant and nobody worries too much about staying up late. You’ve probably already seen a smattering of shower meteors this week, but the peak night will be Sunday (Aug. 12-13) when up to 50 meteors an hour will fly from a dark sky. If you’re closer to a city, cut that number in half. That same evening, watch for a delicate, day-and-a-half-old crescent moon low in the western sky just a half-hour after sunset two fists to the right of Venus.
Brighter Perseids leave glowing trails called trains. Watch this one expand and evolve in this short video.
Perseids (PER-see-ids) get their name from Perseus a fainter constellation that dangles below the familiar W of Cassiopeia in the northeastern sky in late summer and fall. The Perseid meteors appear to radiate from the constellation’s direction the same way rain or snow appears to radiate from a point in front of you when you’re driving through a rain- or snowstorm at night. Only instead of snow, Earth is “driving” through particles left in the path of the comet 109P/Swift-Tuttle.
Some are that debris is made up of really tiny, sand-sized grains, but others are as big as Grape Nuts or sunflower seeds and even larger for the big fireballs. All of them flare to life as meteors when they strike the atmosphere at 37 miles a second (59 km/sec). Brighter Perseids often leave persistent trains. These are white, smoky-looking streaks that quickly fade after the meteor’s passage. Rarely, they can last as long as several minutes as winds in the upper atmosphere twist and stretch them into ghostly shapes.
When a comet particles strikes the atmosphere it strips the electrons off the oxygen and nitrogen molecules it slams into. When the electrons recombine, the molecules give off light. That’s what makes a meteor. The particle itself burns up into a vapor of rock and metal some 70 miles high. The vapor glows briefly but can linger much longer when sodium and iron in the mix react chemically with ozone at that altitude. Long-lasting trains can become faint as they expand, so it’s good to keep a pair of binoculars with you just in case you see one.
Now that you know a little about the shower, let’s get outside. While the peak is Sunday night, Saturday should still provide a modest show. Meteors will appear anywhere in the sky, but I usually face east starting around 10-10:30 p.m. That’s the general direction of Perseus and the radiant. As the constellation rises higher through the night, you’ll see more and more meteors the later it gets. The best time is usually between midnight and dawn. The only equipment you’ll need is a comfortable reclining chair. But I hear hot tubs work, too. I normally spend 1-2 hours outside on the recliner and groove to the twin rhythms of the shower: sudden meteor appearances separated by intervals of quietude.
If the weather’s bad you can watch the shower live online on Gianluca Masi’s Virtual Telescope WebTV starting on Aug. 12 at 3:30 p.m. Central Time (20:30 UT).
Not only the crescent moon but the planets will all be out and the Milky Way will arch high in full glory. Is there any hobby more accessible than astronomy? As long as the sky is clear, the possibilities are limitless.