Aug 7, 2000

Perseid Dawn




The best time to see this year's Perseid meteor shower is just before dawn on August 12, 2000.


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August 8, 2000 -- This weekend our planet will pass through a stream of debris from periodic Comet Swift-Tuttle, sparking a flurry of shooting stars that will be most intense during the hours before dawn on Saturday morning, August 12th.

"It's the Perseid meteor shower and it happens every year around the middle of August," explains Mitzi Adams, an astronomer at the NASA/Marshall Space Flight Center. "Normally the Perseids are one of the best showers of the year. This time the Moon will be nearly full when the shower peaks and it'll outshine the Perseids for most of the night. Fortunately, the Moon sets around 3:30 a.m. local daylight time -- after that observers should have a fine view of the shower until the Sun rises an hour or so later."


Above: Artist Duane Hilton created this fanciful rendition of a colorful Perseid meteor streaking across a moonlit sky on August 12th. The almost-full Moon displays a pinkish hue as the result of moonlight scattered by aerosols from wildfires and dust storms.




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The bright Moon, normally considered a nuisance by meteor watchers, could offer a treat of its own before the meteor display begins. Wildfires in North America and dust storms in Africa have filled parts of our atmosphere with aerosols. A low-hanging Moon seen through such dusty air can take on a beautiful pink or orange hue. The setting Moon also looks much bigger than it does when it's high in the sky -- a trick of the eye known as the "Moon Illusion." So, while you're impatiently waiting for meteors to emerge from the bright moonlight on Saturday morning, don't forget to look for an unusually colorful and swollen Moon as it sinks below the horizon.

After the bright moonlight fades, stargazers could see as many as 100 meteors per hour shooting out of the constellation Perseus in the northern sky. An average Perseid meteor is about as bright as the stars in the Big Dipper, and they are noted for their colorful, long-lasting trails (called "persistent trains" by serious meteor watchers).



The Earth is already in the outskirts of Comet Swift-Tuttle's debris field. Stargazers in early August report seeing 5 to 10 meteors per hour streaming away from the shower's radiant. On August 12th, our planet will move through one or more dense ribbons of debris close to Swift-Tuttle's orbit and the meteor rate will soar.

Perseid meteors pose no danger to people on Earth. Although they strike our atmosphere with a velocity exceeding 130,000 mph, these bits of space dust are extremely fragile and usually smaller than a grain of sand. Meteoroids from Comet Swift-Tuttle completely vaporize in the air about 100 km above Earth's surface.


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Comet Swift-Tuttle last visited the inner solar system eight years ago. As it passed by the Sun in Dec. 1992, solar heating vaporized part of the comet's icy core and created a fresh cloud of dusty debris that triggered unusually intense meteor showers for two years. In August of 1993 and again in 1994 sky watchers across Europe and North America spotted as many as 500 Perseids per hour. Swift-Tuttle faded from view in 1995 and the Perseid meteor shower returned to normal. The comet is now beyond the orbit of Saturn and is not expected to return for another 128 years.


Above: Herman Mikuz captured this image of Comet 109P/Swift-Tuttle on Dec. 15, 1992, just 3 days after the comet made its closest approach to the Sun. The field of view is 2.9x1.9 degrees. Copyright © 1992 by H. Mikuz (Crni Vrh Observatory, Slovenia)

Fortunately, sky watchers needn't wait for the return of Swift-Tuttle in 2126 for another good Perseid shower. The comet's elliptical path around the Sun is almost uniformly filled with dusty debris. When Earth comes close to Swift-Tuttle's orbit each year in mid-August there is always a meteor shower even if the comet is far away. In fact, the Perseids have been seen every year around this time for two millennia.

To catch a glimpse of these reliable meteors, simply wake up early and be outdoors away from bright city lights before dawn on August 12th. As the moonlight fades at 3:30 a.m., the (shooting) stars will come out for early-rising stargazers to enjoy.


Perseid Observing Tips

Perseid meteors stream from a point in the sky (the "radiant") in the constellation Perseus. Because the radiant is so far north -- it is only 32 degrees from the North Star -- the Perseids are rarely spectacular for southern hemisphere observers. An easy-to-recognize pattern of stars near the radiant is "W"-shaped Cassiopeia (see the star map below). Jupiter and Saturn are also not very far away. Shining brightly about 30 degrees above the eastern horizon, the pair will be hard to miss on August 12th.

Below: The radiant of the Perseid meteor shower (pictured here as a red dot) will lie about 50 degrees above the north-northeast horizon at 3:30 a.m. local time on August 12th for observers in the northern hemisphere.


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Most years Perseid meteor watching can begin as early as 10 o'clock at night. The meteor rate increases from 10 p.m. until just before dawn the next morning when the sky above is heading directly into the Perseid meteoroid stream. The 2000 apparition of the Perseids will compete with the bright gibbous moon, so there's not much point in trying to watch before the Moon sets around 3:30 a.m. local daylight time. Before moonset, only the very brightest meteors will be visible. Afterward, stargazers could be in for a brief but beautiful shower.

Experienced meteor watchers suggest the following viewing strategy: Find an observing site as far as possible from urban lights. Bring a reclining chair, or spread a thick blanket over a flat spot of ground. Lie down and look up somewhat toward the north. You don't need to stare directly at the radiant. Perseid meteors can appear anywhere in the sky although their trails will point back toward the radiant, pictured as a red dot in the sky map. Binoculars and telescopes are not essential. The naked eye is usually best for watching meteors, which can streak more than 15 degrees across the sky.  

Web Links


History of the Perseids - trace the history of the Perseid meteor shower from 36 AD to the present day, from Gary Kronk's Comet & Meteors web site.

Comet 109/P Swift-Tuttle - pictures and information about the parent comet of the Perseid meteor shower, from Gary Kronk's Comet & Meteors web site.

"The One Hour only Perseid Comet Litter Meteor Shower" - Jack Stargazer, Episode #00-32


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