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November 18: The Day Of The Leonid Meteors
Chula Vista - Nov 13, 2001 From North and Central America, as well as from Eastern Asia and Australia, people may see a lot of meteors - "shooting stars" - between midnight and dawn of the nights of November 17 to 18 or 18 to 19, provided skies are clear. These meteors belong to the so-called Leonid shower. A first peak, visible from North and Central America, is expected around 9:55 a.m. Greenwich Mean Time on November 18, which is 4:55 a.m. Eastern Standard Time. An activity equivalent to several hundreds to over one thousand meteors per hour (or 10-15 meteors per minute) is expected around the peak time. A second and a third peak are visible from Eastern Asia and, mainly, Western Australia, around 5:24 and 6:13 p.m. Greenwich Mean Time on November 18, which is 1:24 and 2:13 a.m. on November 19. The weaker first peaked is expected to flow over into the stronger second peak, for which an activity equivalent to several thousand meteors per hour (2 meteors per second!) is expected. Notice that American observers should watch in the second part of the night of November 17 to 18, while Asian and Australian observers should watch in the second part of the night of November 18 to 19! The International Meteor Organization, who collects meteor observations world-wide for the purpose of analysis, wishes to point the attention of the public to this spectacular natural phenomenon. The Leonids are caused by a stream of predominantly very small particles, less than 1 mm in size, which orbit the Sun with a period of 33 years, together with their parent comet, Tempel-Tuttle. The orbit of the Leonid particles happens to intersect the Earth's orbit. Each year around November 18, when the Earth is at this intersection, Leonid particles may enter the Earth's atmosphere and cause meteors, popularly called "shooting stars." This year, the Earth will pass through three dense dust trails ejected by the Comet, in addition to several fainter ones. As the predications above are based on models, peak times and peak rates may vary somewhat from the ones quoted above. In particular, there are indications that the first, American, peak may be stronger than quoted here, whereas the second and third, Asian/Australian may be weaker than quoted here. Whereas Europe, Western Asia, and Africa will miss both storms, observers there may still see several tens up to one hundred meteors per hour in the second half of the nights of November 17 to 18 and 18 to 19. Actually, Leonid meteors can be seen every year around November 17. Along the larger part of Comet Tempel-Tuttle's orbit, however, Leonid particles are scattered sparsely, so that, in most years, we see only a few Leonid meteors per hour. Only in the vicinity of the Comet, the density of Leonid particles is much higher. Therefore, we observe much higher Leonid activity every 33 years during a couple of years, when Comet Tempel-Tuttle revisits our region of the Solar System. In some instances, we even see a real meteor storm! Old chronicles contain references to past Leonid meteor storms back to the 10th century A.D. The best-known Leonid meteor storms are those of 1833 and 1966, when tens of meteors per second darted across the skies during the peak hour! The 1833 meteor storm was so spectacular that it in fact launched meteor research as a branch of astronomy. Since the 1966 meteor storm, Comet Tempel-Tuttle has completed another revolution around the Sun. The passage of the Comet through its closest point to the Sun on February 28, 1998 marked the beginning of a five-year period (1998-2002) during which strongly increased Leonid meteor activity is again possible. Although 1998 gave us an unexpected (but meanwhile convincingly explained) fireball shower, the first storm in the present Leonid epoch occurred in 1999, with a peak activity around 60 meteors per minute (yielding an equivalent hourly rate of almost 4000). In 2000, no storm was seen, but several peaks with a few hundred meteors per hour occurred. Observations in 1999 and 2000 matched the predictions by astronomers David Asher and Robert McNaught really well, so that there is more than good hope that the predictions for this year are reliable, too. In order to see meteors, the sky must be clear and the selected observing site should preferentially be free of light pollution; the less light, the more meteors will be seen! Notice that Leonid meteors occur in the second half of the night. Hence, there is no point in starting an observation much earlier. Die-hards who do not want to miss anything of the show should then continue to watch until dawn. People who cannot afford to stay up that long should focus on a period of, say, one to two hours centered around the predicted peak time for their region. Mind that it can be very cold in mid-November: warm clothing adapted to the local climate is essential! For comfortable observing, use a reclining chair, and install yourself in a suitable sleeping bag or under several blankets. While observing, do not fix a particular star, but look relaxedly and patiently to a wide area of sky and wait for shooting stars to appear. Related Links International Meteor Organization Leonids 2001 at Sky & Telescope Local Leonid Estimator Leonids In The Southern Hemisphere SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express
Comet Borrelly: The Data So Far
Pasadena - Nov 13, 2001After introducing another member of the solar system family to Earth, Deep Space 1, the little spacecraft that could -- and did! -- continues flying contentedly in its orbit around the Sun. Meanwhile, scientists are analyzing the fantastically rich harvest of data returned from the historic encounter with comet Borrelly. More than two years after the end of its 11-month primary mission, on September 22 DS1 stepped up to its greatest challenge of all with the elegance and skill of a true master. The encounter certainly did not go the way I expected -- instead, everything went perfectly! |
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