I was so busy looking down yesterday I forgot to look up. If you’ve been staying up late and noticing more meteors than usual, it’s because the Southern Delta Aquariid meteor shower’s been active this month. They don’t come in droves, only about 10 to 20 per hour under dark skies, but they mark the general increase in the number of meteors we’ll see over the next month or so.
The Delta Aquariid meteor shower peaked this morning, but before you start throwing tomatoes (or better, meteorites) at me for not reminding you sooner, the peak’s not a one-night affair. You’ve probably been watching Delta Aquariids for the past week without even knowing it. The shower’s active from July 21 through August 23 with a peak lasting several days centered on July 30.
Because the radiant — the spot in the sky from which shower meteors radiate or appear to originate — doesn’t rise until around 10:30 p.m. local daylight time, the “Deltas” are best viewed after midnight in the wee hours before dawn. The best time is from 2-4 a.m. when the radiant in Aquarius is highest in the southern sky. The hour’s a little painful I realize, but it’s also when the moon’s out of the sky, making for ideal viewing circumstances.
Most meteor showers are small apple-seed to small pebble-sized fragments of comets that crumble off material when heated by the sun. The Delta Aquariids originated with the breakup of one or more sungrazing comets that passed so close to the sun they broke to pieces. Each July-August, Earth plows into the cloud of debris and bits and pieces strike the atmosphere at 90,000 mph (41 km/sec). The crumbs vaporize into fine dust and leave momentary streaks of glowing air — meteors — that give us a thrill. They also remind us that Earth’s as much in touch with space as all the other creatures of the night sky.
Let’s go over the details. You’ll want a reclining lawn chair and jacket or blanket to stay warm as you lay still and observant. The best viewing is away from city lights (as far as you can swing it) and when the moon has set. Kick back and face south or east. Click here to find moonset time for your town. For the next few nights, the moon sets between 12:30 and 2 a.m. local daylight time. The last good morning will be August 4. After that, the moon’s up from dusk till dawn.
The Southern Delta Aquariids are the warm-up band for the grander, richer Perseid meteor shower which peaks in the early morning hours of Saturday morning, August 12 with Saturday night looking nearly as good. Great timing, since many of us have the day off and can afford to lose a few hours of sleep. But the moon will throw a wrench in things. It’s only four days past full in waning gibbous phase and will rise around 11 p.m. While it won’t kill the brighter meteors, it will blank out the fainter ones, so I expect that meteor tallies will be lower this year than the normal 80 meteors per hour visible from a dark, moonless sky.
But that won’t stop you from going out for a look. I mean it’s summer, and the August nights are pleasant. We won’t be able to help ourselves. I’ll have more on the Perseids as we get closer to the date.