The Perseid meteors, generally the most reliable of the four or five major annual showers, should be at their best during the night between August 12 and 13.
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The meteors are solid particles incandescing as they enter Earth’s atmosphere. They separated, perhaps centuries ago, from periodic Comet 109P Swift-Tuttle, which returns about every 130 years and last came around in 1992.
Such streams gradually spread – they could be thought of as comet tails that have exploded in size – and Earth takes more than a month to pass through the Perseid stream, so outlying meteors may have been seen from as early as July 17.
The radiant is the point or small area from which the meteors in their parallel courses appear to fly out to all parts of the sky. It is in the head of the constellation Perseus, but moves slightly eastward from night to night as Earth moves along its orbit through the meteor stream. You know a “shooting star” is a Perseid, and not a sporadic space particle, if its streak, in whatever part of the sky, points backward to Perseus.
The peak of the shower, when we move through the densest part of the stream, is expected to be on August 12, but this is typically somewhat unpredictable for meteor showers, and the Perseids can have several peaks because of variations within the stream.
Besides weather, moonlight is the obscurer of meteors, drowning out the fainter ones. This time the Moon is only about 4 days old and over in the west, setting not long after sunset.
A metric for the abundance of a meteor shower is its “zenithal hourly rate,” and the Perseids are credited with a ZHR or 110. This means the number an alert observer might count in an hour if sky conditions were perfect and the radiant directly overhead – conditions rarely met. So the number you see will probably be lower. They could average around one a minute – not, of course, at regular intervals. Remember that these streaks are bits of dust, sand, possibly rock, hundreds of miles apart.
Notice that the Perseids come from the same general direction as the point marked “Earth’s direction of travel” under the horizon in our sky scene. In other words, the meteors hit the front, or morning, side of Earth, because their orbit and the comet’s are retrograde: opposite in direction to Earth’s. This makes them among the swiftest in plowing into our atmosphere; and more of them are seen after midnight, as is the case for many meteor showers.
In our sky scene before midnight, the radiant is rising into view, and it will slant upward, parallel to the celestial equator, till the pre-dawn hours. The higher the radiant is in the sky, the more likely are meteor streaks to be above the horizon.
This space view from ecliptic north shows the meteor stream, or rather one thread of it, meeting Earth from north of head on. A broad arrow represents Earth’s flight along its orbit in 3 minutes, and an arrow on the equator shows how far it rotates in 3 hours. America has entered night, and is rotating toward a high head-on view of the stream in the small hours of the morning.
Usual advice is to dress warmly for lying out at night awaiting meteors. In August, and in the new era of heatwaves, a sweater may be superfluous, but you can take it off and use it as a pillow.
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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format. You may be able to enlarge them on your monitor. One way: right-click, and choose “View image”, then enlarge. Or choose “Copy image”, then put it on your desktop, then open it. On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers). Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.
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According to spaceweather.com, an unexpected intense outburst of Perseid meteors was observed from North America on the night of August 14, up to three or four meteors per second. This was one night after the predicted peak, leading to speculation that Earth might have passed through the fabled “Perseid filament”, a dense stream of comet dust that doesn’t disburse because it is in a resonant orbit with Jupiter. Or maybe it’s a new filament. Worth watching for next year.
https://spaceweather.com/archive.php?view=1&day=19&month=08&year=2021
I saw exactly one Perseid meteor this year. Monday August 16 was the one evening in the past few weeks when the sky wasn’t obscured by clouds or haze from the wildfires. The meteor was a dramatic long streak all the way over to Virgo in the southwest, brighter than first magnitude! So I can say I saw the Perseid meteor shower this year.
Thanks, Anthony, The photos are almost reminiscent of the Leonid storms of the past. Interesting indeed about the filament. It’s enjoyable to picture these moving structures in space. Also to imagine a comet disbursing coinage as it travels along!
Had a view of Perseus last at about 2240 low in the north east but nothing meteors I had my phone mounted on a tripod at the ready to capture something but clouds moved in by 23hr..I did capture a streak a few nights back that photo bombed me capturing M31 but I think that it might have been some of the space junk plutocrat Musk is putting up ,virtually unregulated ,into space so people in Guinea Bissau can watch a Game of Thrones,if they can afford his disks!All allegedly to fund his Martian ambitious and nothing to do with making a fast buck.
1992 to 2021 isn’t 130 years. Did you mean 30 years?
No. The comet is not returning this year; it’s the meteors that we see every year.