HOMEPAGE OBSERVING by Alan MacRobert
The Perseid meteor shower has put on a fine show for millions of people over the last two nights — just as predicted. Despite the interfering light from a last-quarter Moon, millions of people who rarely watch the sky came away entranced by spotting the occasional, graceful shooting stars, judging by news reports and internet chatter. This year's display even delivered the spike in activity expected to occur around 8h Universal Time (3 a.m. CDT; 1 a.m. PDT) on the morning of August 12th.
"The wife, daughter and I set up camp in the back of the pickup here in Livermore [California] last night for a star show my 11 year old daughter will never forget," writes a commenter named Deadzheadz. "From 9:30 until 11 p.m. we spotted 25 to 30 meteors coming down. Some were so long and bright we had to turn our heads to follow the complete tail."
Not so many people used to do this, by the way. One of the things I've been proud of in my years at Sky & Telescope is helping to popularize meteor-watching as something that anyone can do — if they're told when and a few basics of how. A couple decades ago we started sending out press releases to news media about the Perseids, the December Geminids, and the November Leonids (during the span from 1998 to 2001 when they were going great guns). Maybe we helped train all those reporters and TV meteorologists; nowadays they pick up good shower predictions from many sources on their own, and usually get it right.
Of course, the Internet has helped immensely. For example, you can watch the amateur-based International Meteor Organization's preliminary counts piling in from around the world around the clock; take a look. We used to have to wait months for this.
And amateurs keep innovating — see for example this near-real-time activity curve compiled by Chris Peterson of Guffey, Colorado, based on his fisheye-lens video camera monitoring his whole sky. It documents the brief increase around 8h UT August 12th.
During a 20-minute period around this peak (from 8:10 to 8:30 UT, in moonlight), Ernie August says he saw "8 Perseids ranging from 3rd magnitude to 0 magnitude. The highlight was a 1st-magnitude 'point meteor' [one headed straight at the observer] that looked like a star flashing on and off. This occurred in western Perseus near the location of NGC 1528. . . . Another highlight was two 1st-magnitude meteors occurring one right after the other and moving in the same direction."
The usual advice for visual observers is to watch a meteor shower when its radiant (the shower's perspective point of origin) is high in the sky. For most showers, including the Perseids, this means watching during the inconvenient early-morning hours. Fewer meteors appear earlier in the night, when the radiant is lower.
However, there is a compensating effect. Meteors that come from a low radiant are "Earthgrazers," meaning they skim along for a great distance across the upper atmosphere. These can be truly spectacular, as the description from Deadzheadz attests. Here's another, from veteran California amateur Derek Breit:
"From 9:30 to 11 p.m. PDT [August 12th] I saw at least two dozen bright Earthgrazers that traveled across at least 60° of sky . . . most covering 70° to 90°. Almost all traveled right down the meridian as seen from Morgan Hill. Second best show of meteors I have ever seen."
See more pictures in the Perseid photo gallery at Spaceweather.com.
During 8 hours on the night of August 11–12, Chris Peterson of Guffey, Colorado, ran an all-sky video camera equipped with a fisheye lens. He combined the 96 brightest Perseid meteors into this composite image. The circle gives the azimuth (compass directions) around the horizon. Click here for details and a larger view.
Not so many people used to do this, by the way. One of the things I've been proud of in my years at Sky & Telescope is helping to popularize meteor-watching as something that anyone can do — if they're told when and a few basics of how. A couple decades ago we started sending out press releases to news media about the Perseids, the December Geminids, and the November Leonids (during the span from 1998 to 2001 when they were going great guns). Maybe we helped train all those reporters and TV meteorologists; nowadays they pick up good shower predictions from many sources on their own, and usually get it right.
Of course, the Internet has helped immensely. For example, you can watch the amateur-based International Meteor Organization's preliminary counts piling in from around the world around the clock; take a look. We used to have to wait months for this.
And amateurs keep innovating — see for example this near-real-time activity curve compiled by Chris Peterson of Guffey, Colorado, based on his fisheye-lens video camera monitoring his whole sky. It documents the brief increase around 8h UT August 12th.
During a 20-minute period around this peak (from 8:10 to 8:30 UT, in moonlight), Ernie August says he saw "8 Perseids ranging from 3rd magnitude to 0 magnitude. The highlight was a 1st-magnitude 'point meteor' [one headed straight at the observer] that looked like a star flashing on and off. This occurred in western Perseus near the location of NGC 1528. . . . Another highlight was two 1st-magnitude meteors occurring one right after the other and moving in the same direction."
The usual advice for visual observers is to watch a meteor shower when its radiant (the shower's perspective point of origin) is high in the sky. For most showers, including the Perseids, this means watching during the inconvenient early-morning hours. Fewer meteors appear earlier in the night, when the radiant is lower.
However, there is a compensating effect. Meteors that come from a low radiant are "Earthgrazers," meaning they skim along for a great distance across the upper atmosphere. These can be truly spectacular, as the description from Deadzheadz attests. Here's another, from veteran California amateur Derek Breit:
"From 9:30 to 11 p.m. PDT [August 12th] I saw at least two dozen bright Earthgrazers that traveled across at least 60° of sky . . . most covering 70° to 90°. Almost all traveled right down the meridian as seen from Morgan Hill. Second best show of meteors I have ever seen."
See more pictures in the Perseid photo gallery at Spaceweather.com.
Posted by Alan MacRobert, August 13, 2009
No comments:
Post a Comment