Post by Chicago Astronomer - Astro Joe on Aug 8, 2004 16:14:28 GMT -6
The Perseid Meteor Shower - August 2004
It's that time of year again, when the skies open up and rain down space debris over our heads. The Perseids have returned.
On August 11th and 12th the annual Perseid meteor shower will be at it's peak and not to be missed.
This year, the show should be a better than average one for Chicagoans, as the moon will not interfere and add to the light pollution, obscuring fainter meteor streaks. The particles that Earth will be plowing through originates from Comet Swift-Tuttle, mostly sand grain size, but sometimes larger marble size pieces burn up in our atmosphere and those are the ones to look for. They light up very bright and sometimes leave a smoke trail. As the orbit of the comet leaves a trail of debris behind it... this years the filament trail will be right in the path of our Earth.
First...Some background
The filament, like the rest of the dust in the Perseid cloud, comes from Comet Swift-Tuttle. The difference is, the filament is relatively young. It boiled off the comet during the Civil War, in 1862. Other dust in the cloud is older (perhaps thousands of years old), more dispersed, and responsible for the month-long shower that peaks on August 12th. The filament will eventually disperse, too, but for now it retains some of its original ribbon-shape.
The first record of the Perseid meteor shower comes from a Chinese manuscript written in A.D. 36. Lewis Swift (Marathon, New York, USA) discovered this comet in 1862 July 16, while examining the northern sky with his 11.4-cm Fitz refractor. He described the comet as a somewhat bright telescopic object, but did not report it since he thought he was observing the comet Schmidt had found on July 2. Without knowledge of Swift's observation, Horace Parnell Tuttle (Harvard College Observatory, Cambridge, Massachusetts, USA) independently discovered this comet on July 19 and noted it was heading northward. He then made an official announcement. When Swift heard of Tuttle's find, he immediately realized the comet seen on July 16 was not Schmidt's and made his announcement to get credit for his first comet discovery.Comet Swift-Tuttle was last seen in 1862. Its orbit was then calculated to have a period of about 120 years.
It was predicted to return in 1982 but was not observed. Minor searches for the comet began in 1980, which was within the error range given by calculations, and more rigorous searches were conducted in 1981 and 1982, but nothing was found.Because of this, there was speculation that the comet had disintegrated. This theory was supported by its association with the Perseid meteor stream. Tsuruhiko Kiuchi (Japan) discovered the comet on September 26, 1992 and reported it to the National Astronomical Observatory (Tokyo). He said it was magnitude 11.5. and almost 10 years away from its expected position. The chance of a collision would be very small even though the Earth does pass through the orbit of the comet. The comet will be moving at a speed, relative to the Earth, of 60 kilometres per second. This means that there is only a time of a few minutes during which a collision is possible.
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If predictions are correct, Earth will plow through the filament on Wednesday, August 11th at 2100 UT (4 p.m. CDT). This will produce a surge of mostly-faint meteors over Europe and Asia. Observers might see as many as 200 meteors per hour.
But here in Chicago - start looking to the East NorthEast at dusk, this is when "Earth Grazers" skim the atmosphere like a rock across a pond and can produce great fireballs. You'll see more as the evening progresses, especially after midnight as we run directly head on into the debris field. As the meteors disintegrate, the dust it leaves behind will gently fall and settle all around us. We inhale, consume and walk amongst space dust everyday. Think about that the next time you dust.
If you catch some meteors, please do write in about it and share with all of us.
