Artist Duane Hilton's concept of a Lyrid meteor over Death Valley
Apr. 21, 1999: Stargazers in recent months may have noticed something missing from the nighttime sky: shooting stars. Each year between January and April there is a lull in meteor activity as Earth passes through a part of its orbit that is free from major cometary debris streams. Without much space dust in the area, there are simply fewer cosmic particles burning up in the atmosphere to produce visible shooting stars.
Above: Artist Duane Hilton created this nighttime painting of a Lyrid meteor streaking over sand dunes in Death Valley, CA.
It's been a long 3 months for meteor enthusiasts, but the 1999 intermission in meteor activity is nearly over. It ends this Thursday with the arrival of the annual Lyrid meteor shower. The Lyrids will peak at 1600 UT (9 a.m. Pacific Standard Time) on April 22 with at least 10-20 meteors per hour. The predicted peak occurs during daylight on Thursday morning across most of the United States, but the rate of meteors should still be high a few hours earlier before the sun rises. No matter where you live, the best time to look will be during the hours before dawn on Thursday after the waxing quarter Moon has set. Typical Lyrid meteors are nearly as bright as the main stars in the Big Dipper, which makes it a good shower for both beginning and experienced observers.
Most years, observers of the Lyrids can expect to view one or two shooting stars every few minutes. That's just a trickle compared to the avalanche of shooting stars and fireballs seen by millions during the 1998 Leonids meteor shower, but the Lyrids are not always so meek. In 1982, for example, over 90 meteors per hour were seen for a brief time. An even bigger outburst in 1803 was documented by a journalist in Richmond, Virginia who wrote:
"Shooting stars. This electrical phenomenon was observed on Wednesday morning last at Richmond and its vicinity, in a manner that alarmed many, and astonished every person that beheld it. From one until three in the morning, those starry meteors seemed to fall from every point in the heavens, in such numbers as to resemble a shower of sky rockets..." [ref]
Another account quoted an observer who "counted 167 meteors in about 15 minutes, and could not then number them all." [ref]
Although the Lyrids are not usually so spectacular, they are notable as the oldest recorded meteor shower. Lyrids have been observed for at least 2600 years, according to Chinese records from 687 BC describing "stars that fell [like] rain."
The Lyrid meteor stream is asscociated with periodic comet Thatcher C/1861 G1, whose orbit is tilted nearly 80 degrees with respect to the plane of the solar system. Because the comet spends most of its time well away from the planets, it is nearly immune to significant gravitational perturbations. This is probably the reason why the debris stream has remained stable and the Lyrid shower has been observed for so many centuries.
based on http://science.nasa.gov/science-news/science-at-nasa/1999/ast21apr99_1/
No comments:
Post a Comment