The Great Meteor Shower of August

The Perseids are rising toward one of the best of their annual displays.

ho150812ev120

You may see a few of these light-streaks any night from about July 17 to August 24, but they increase gradually to a peak, predicted, this year, for August 13 at 6 Universal Time. That is 7 AM by British clocks, 2 AM in eastern North America. And there are often sub-peaks before the main one, caused by slightly thicker threads in the vast diffuse stream of particles in space through which the Earth is passing.

The exact time is not what matters most, though it happens to be excellent this year for North America and Europe. You can be out watching, in the night between Aug. 12 and 13, preferably as late as possible in that night, but you may also see Perseids in the surrounding nights. (I meant to get this post ready yesterday but my cat prevented it.)

Why as late as possible in the night? (Which could mean 3 or 4 AM if you’re an enthusiast.) The “radiant,” the spot in the constellation Perseus from which these meteors seem to shoot, is in the sky all night, but at first it is low in the northeast; as the night goes on and Earth turns, that part of the sky swings higher, so more of the meteor trails are likely to be above the horizon for you. After midnight is better; best of all is around 5 or 6 AM, when the radiant is almost overhead.

(That’s the way things are for us on the northern side of Earth’s globe. Southerners are unlucky, they don’t get to see the Perseids. The globe is in the way.)

Find a non-cloudy time, find a dark place away from light pollution (sadly difficult in modern times); make yourself comfortable (keep warm). It may take twenty minutes for your eyes to adapt to the dark. Sit back and gaze tranquilly at, say, a direction northeastward and half way between horizon and zenith, but there’s no need to stare fiercely at any particular spot: it will suffice to be dreamily attentive to your sky surroundings. Then you may see nothing for a while; a sudden faint streak over here, a longer and brighter over there; nothing for a while; a flurry of Perseids like a quiet firework; you may miss some behind you, that doesn’t matter. If you count, you could get fifty an hour at the best time, maybe even more, but neither I nor the hero Perseus make promises.

What is especially favorable this year is that there is no light pollution from the Moon, which when in the sky can drown out all but the brightest meteors. It is a day before New: in the direction of the Sun, out of the way.

What are these “children of Perseus”? They are bits of dust and rock that separated, most of them many centuries ago, from a 16-mile-wide flying mountain called Comet 109P Swift-Tuttle. It was discovered in July 1862 by Lewis Swift and three days later by by Horace Tuttle. “109P” means that it was the 109th comet to be recognized as “periodic”: returning in an elliptical orbit. It didn’t come by again till 1992, for its period is long, about 130 years. This means the orbit is vast; its outer end is at about 52 astronomical units (Sun-Earth distances), way beyond Neptune’s 30. So it is amazing that the comet, diving from such a distance, comes so close to Earth’s little orbit.

\metSfPer

In fact, it seemed to come dangerously close, and at the next return, in 2126, Earth will be close to that point in its orbit, so – impact? This prompted Gary Kronk, an amateur but a great expert and author on comets and meteors, to make a study of ancient records, which might turn up other appearances of the comet and thus help to refine calculations. And he found that indeed the Chinese had observed it in 69 BC and AD 188. (It is now also identified with a comet of 1737.) This enabled Brian Marsden to calculate a more accurate orbit for the future. On 2126 Aug. 5 the comet will pass 0.15 a.u., not 0.05, from Earth and there will be no danger, but it will be like a naked-eye bright star. There will be a probably closer passage, and slightly higher chance of collision, in September 4479.

 

7 thoughts on “The Great Meteor Shower of August”

  1. The Perseid meteor shower has become too popular.

    For the past few years when the lunar phase has favored the Perseids I’ve camped for a couple of nights at Mt. Diablo State Park. There’s a nice open hillside beside the campground, perfect for meteor watching. I set up a telescope and show my fellow campers other things in the sky while waiting for the sky to get dark enough for meteors (Saturn was a big hit this year).

    This year there were more than twice as many people at the campground specifically for the meteor shower than previously. That open hillside was filled to comfortable capacity. There were several groups of loud twenty-somethings for whom meteor watching seemed to involve mostly staring at the brightly glowing screens of their mobile phones. And people of all ages were continually using LED flashlights bright enough to guide aircraft landings. In morning-after conversations, several people said they had enjoyed seeing meteors, and a less light-polluted sky than they’re used to, but about as many said they were disappointed that they didn’t see more meteors, and that the meteors weren’t brighter and more spectacular — in fact there had been a few dramatic grazing meteors early in the night, and a good number of more direct meteors later at night — I didn’t count, but I would guess at least 30 to 40 an hour between midnight and when I went to sleep around 3 am DST. The dissatisfied seemed to have over-inflated expectations of a fireworks show.

    I’m considering starting a campaign to badmouth the Perseids, emphasizing that the hourly rate of Perseid meteors has been declining since Swift-Tuttle’s 1992 perihelion, and will continue to shrink until 2126.

      1. Most of the public campgrounds within a two-hour drive of my home are either in forests or under coastal fog, or both. And unfortunately mobile phones and LED lights seem to have become appendages for a significant number of people. I was dismayed to see several people using their flashlights during bright twilight. These people seem never to have experienced dark-adapted vision. It’s sad.

        1. If you go to the Texas Star Party and turn on any light that isn’t red, you’ll be run off. Perhaps signs in state parks: “Shine no lights except red ones – then you’ll be able to see the stars.”

  2. We were lucky with the weather and were able to spot a meteor every 1, 2, or 3 minutes. They came in all sizes and brightnesses. This was from 12 to 2 a.m., EDT in the US. It was a great display, for sure!

Leave a Reply to Carlos Herranz Cancel reply