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 December 16, 1998:
When the Geminid meteors first appeared in the mid-1800's they were
unimpressive. Those early showers boasted a
mere 10-20 shooting stars per hour, barely above the background
level of sporadic meteors.
Since then the Geminid meteors have grown in number until
today they make up one of the most spectacular annual showers. In 1996,
the last time the Geminids appeared in a dark moon-less sky,
observers saw as many as 110 per hour. According to preliminary
reports from more than 40 sky-watchers, this year's shower
was even better, peaking at 140 +/- 40 meteors per hour
(zenithal
hourly rate) during the morning of December 14.
Above, right: "Geminid meteors in Orion" -- Clicking on the image above will activate a video clip of two meteors streaking through the constellation Orion. They were filmed by Dr. Tony Phillips in Aspendell, CA at approximately 1110 UT on December 13, 1998, the night before the maximum of the 1998 Geminid meteor shower. He used an Astrovid 2000 CCD video camera with a 12 mm f1.2 lens, and a shutter speed of 1/60 sec. The 30 frame sequence spans 2 seconds of actual time. The dimmer of the two shooting stars, which travels straight down from the top of the image, is a Geminid. The brighter, which zooms in from the left, comes from the general direction of the constellation Leo. It is probably a sporadic meteor or a Coma Berenicid, but it could also be a late-arriving Leonid. |
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According to reports from experienced meteor watchers only a few of the 1998 Geminids left "persistant trains." Like the meteors in the video above, they generally appeared to be compact, moving points of light rather than elongated streaks. In this respect the Geminids differed from last month's Leonid meteors which often produced long-lasting brightly colored meteor trails. One reason for the difference may be that Geminid meteoroids are relatively slow-moving and deposit less energy into Earth's atmosphere. Leonid meteoroids strike the atmosphere at 72 km/s but the Geminids travel only half as fast, at 36 km/s. |
| There is a widely-held notion that slower-moving meteoroids produce brighter fireballs because they penetrate to lower, denser levels of the atmosphere before they disintegrate. If that were correct then one might expect more fireballs and persistant trains from the Geminids, rather than less. However, the origin of meteor trains and their colors is an area of active research in meteor astronomy. Many of the basic properties of meteors are still a mystery. |
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in Discovery 
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The 1998 Geminids were also notable for coming in bunches.
Groups of shooting stars consisting of
2 or 3 meteors were common, and one professional astronomer reports
observing a group of 6 or more emanating in a starburst pattern from
the radiant, near the star Castor.
This account from long-time meteor observer Mark Balzer in Oklahoma is typical of the reports received so far: "This shower is one of the best I've seen in my 25 years of observing meteors, but not as good as the Leonids less than a month ago. Some of the meteors are fairly bright, up to magnitude -1 (not as bright as many Leonid meteors), but none are leaving lasting trails.... The meteors sometimes appear in groups of two or three. These groups may consist of meteors in the same part of the sky or observed simultaneously (or nearly so) in different parts of the sky." |
1999: A good year for Geminids?The source of the Geminid meteoroids is a curious object called 3200 Phaethon that looks like an asteroid, but may be an extinct comet. It travels in a highly elliptical 1.4 year orbit that brings it within 0.15 AU (astronomical units) of the Sun. Phaethon will pass through the inner solar system next year, coming within 1.2 AU of Earth on October 16th. If 3200 Phaethon is indeed the source of the Geminid meteoroids, then its close approach to Earth next year bodes well for another impressive Geminid shower in 1999. |
 Take a virtual tour of the solar system, complete with the curious asteroid 3200 Phaethon, the source of the Geminid meteors. |
| Web Links | |
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NASA Liftoff meteor shower pages - learn the basics about meteor showers. Includes tutorials, Java animations, and educational activities. Eyewitness accounts of the historic 1966 Leonid storm -- an Ames Research Center Archive Satellite Tracking - monitor satellites as they weather the storm NASA's Office of Space Science - press releases and other news related to NASA and astrophysics External Links: The Geminids -- from Gary Kronk Meteors and Comets web site December's generous Geminids -- Sky &Telescope article |
Related Stories: 27 Nov. 1998: A bust or a blast? -- New images of 1998 Leonid fireballs and their smokey remnants.23 Nov. 1998: Leonids Sample Return payload recovered! -- Scientists are scanning the "comet catcher" for signs of Leonid meteoroids. 19 Nov. 1998: Early birds catch the Leonids -- The peak of the Leonid meteor shower happened more than 14 hours earlier than experts had predicted. 18 Nov. 1998: A high-altitude look at the Leonids -- NASA science balloon catches video of 8 fireballs. 16 Nov. 1998: The Leonid Sample Return Mission -- NASA scientists hope to capture a Leonid meteoroid and return it to Earth. 16 Nov. 1998: NASA Spacecraft take cover from the Leonids -- but the Hubble Space Telescope won't stop observing. 10 Nov. 1998: Great Expectations: the 1998 Leonid meteor shower -- the basics of what the Leonids are and what might happen on November 17. |
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