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Giacobinids dazzle observers Outburst occurred over Japan, East Asia

October 14, 1998: Sky watchers in Japan and eastern Asia were treated to a spectacular show last week thanks to periodic comet Giacobini-Zinner. The comet is about 40 days away from Earth's orbit, but tiny bits of debris from the comet arrived last Thursday. Astronomers had predicted a possible meteor storm and many observers were not disappointed.

Giacobinid outbursts have happened in the past with hourly rates greater than 20,000. The year's outburst occurred between 13h and 14h UT (Universal Time) on October 8th. That's between 6 and 7 a.m. in California and 9 and 10 a.m. in New York. In most of the US the meteor shower was nearly impossible to see in the morning sunlight, but in Japan observing conditions were far better. The Nippon Meteor Society reports that over 500 meteors per hour were seen around 8:30 pm local time in Japan. Although the outburst was difficult to see in the US, it was not impossible. An avid meteor watcher in Kansas City, MO reported this description of a bright meteor he saw on 8 October at 12:14 UT: "[It] appeared approximately 30 degrees above the north horizon. It was white with a slight steel blue color in it. What was most amazing was the fact that the sun had already lit up a clear morning, but had not yet come over the horizon...the meteor was big and brilliant enough to be seen easily."

Artist's concept of a streaking Giacobinid fireball. Courtesy Duane Hilton, Bishop Web Works.

The plot shows the number of meteors per hour counted by members of the Nippon Meteor Society in Japan. The maximum rate was over 500 per hour. Click on the image for a larger plot

Some observers more fortunate than others The meteor outburst lasted less than about 2 hours, so while Japan and Asia saw more than 500 per hour observers elsewhere saw very few. A team of nine experienced observers from the Israeli Astronomical Association contributed this report to Science@NASA: "During the almost three hours of observing we counted a very low rate of meteors - about 5 to 7 per hour during the first hour, and then 1 to 2 meteors per hour during the proceeding hours. It seemed that even sporadic meteors, let alone Giacobinids, disappeared from the sky."

Giacobinid Radio Meteors Increasingly, amateur astronomers are tuning in to meteors through radio echoes and last week's shower was no exception. When a meteor burns up in the atmosphere it leaves behind a trail of ionized gas. The ionization rapidly dissipates, but transmissions from distant radio stations are briefly reflected from the ionized trail back down to Earth. During an intense meteor shower, a simple shortwave receiver can detect many echoes per minute from stations thousands of kilometers away.

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During last week's Giacobinid outburst, E. P. Bus from Groningen, Netherlands used a 3-element Yagi antenna to observe hundreds of meteor reflections. The signals he detected were transmitted at 72 MHz from a 130 kilowatt station in Wroclaw, Poland. The transmissions from Poland traveled upwards into the atmosphere, bounced off the ionized meteor trails, and traveled back down again to the antenna in the Netherlands. The plot below shows preliminary counts for reflections lasting longer than 1 second. Bus observed a peak in the number of meteors per hour at about 12:30 UT, consistent with the visual observations in Japan. Note that in the Netherlands the Giacobinid outburst happened during daylight hours when visual observations were practically impossible. Radio waves were the only way to "see" the meteor storm. More information can be found at the Dutch Meteor Society web site.

Explore a 3D Model of Comet Giacobini and the inner Solar System Java Required Take a 3D tour of the 9 planets as comet Giacobini-Zinner passes through the inner solar system! This Java applet from NASA Liftoff lets you watch the comet as it whizzes by Earth on its journey around the Sun.

Comet Rubble When comets visit the inner solar system, they are warmed by the sun and pitted by the solar wind, which produces the familiar tails that can often be seen with the naked eye when comets approach the earth. This debris is left in space, and is comprised of tiny particles of ice and rock. When Earth encounters these particles they strike the atmosphere and become shooting stars. Early last week scientists were still unsure whether or not debris from Giacobinid-Zinner would produce a noticeable storm. That's because Earth was approaching the orbit of Giacobini-Zinner 49 days earlier than the comet itself. We know that comets leave debris behind them, but does debris fly ahead of the comet as well? Based on last week's meteor outburst, and thanks to the efforts of meteor observers worldwide, we now know the answer is "yes". Our improved understanding of the Giacobinids will make it possible to more reliably predict meteor storms in the future, and will help scientists understand meteor streams and their parent comets.

Web Links
More science headlines - NASA space science research Tune-up for the Leonids - posted Oct 7, discusses the astronomy of the Giacobinids Meteor Showers - Washington University in St.Louis Discovery of the Perseid Meteors - by Mark Littman, adapted from Sky and Telescope	Satellite Tracking - monitor satellites as they weather the storm International Meteor Organization  NASA's Office of Space Science - press releases and other news related to NASA and astrophysics

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