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FWD: [UASR] Fine Leonid Meteor Displays Predicted Through To 2002

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  • Frits Westra
    Posted by : [UASR] Perry J. van den BrinkFine Leonid Meteor Displays Predicted Through To 2002From Jacqueline Mitton
    Message 1 of 1 , Sep 1, 1999
      Posted by : "[UASR]>Perry J. van den Brink" <owner-uasr@...>

      Fine Leonid Meteor Displays Predicted Through To 2002

      >From Jacqueline Mitton <jmitton@...>


      Date: 30 August 1999
      For immediaterelease

      Ref. PN 99/27
      Issued by: Dr Jacqueline Mitton
      RAS Press Officer
      Phone: Cambridge ((0)1223) 564914
      FAX: Cambridge ((0)1223) 572892
      E-mail: jmitton@...

      RAS Web: http://www.ras.org.uk/ras/

      * * * * * * * * * * * * * * * * * * * * * * * *


      Dr David Asher (dja@...)

      Professor Mark Bailey (Director: meb@...)

      Mr John McFarland (PR Officer: jmf@...)

      Armagh Observatory, College Hill, Armagh, BT61 9DG
      Tel: 028-3752-2928, Fax: 028-3752-7174

      Dr Rob McNaught (rmn@...)
      School of Astronomy and Astrophysics, Australian National University.

      * * * * * * * * * * * * * * * * * * * * * * * * *


      November's Leonid meteor shower will produce good displays this year
      and next, and strong storms of meteors in 2001 and 2002, according to
      new research by Dr David Asher, of Armagh Observatory, and Dr Rob
      McNaught of the Australian National University. Writing in the Monthly
      Notices of the Royal Astronomical Society (21 August 1999 issue), they
      show how the times when Earth passes through the dense streams of
      matter in space that produce meteor showers can now be predicted with
      remarkable accuracy.

      In the early hours of 17th November last year (1998), meteor watchers
      awaiting the Leonid shower were taken by surprise when a spectacular
      display of bright meteors occurred 16 hours before the predicted time
      for the maximum of the shower. The explanation for this phenomenon was
      discovered by Dr Asher and his colleagues Professor Mark Bailey of
      Armagh Observatory, and Professor Vacheslav Emel'yanenko of South Ural
      University, Chelyabinsk, Russia, and was published in April (see RAS
      Press Notice 99/09). They showed that the bright meteors were seen when
      Earth passed through a dense arc-shaped cloud of particles shed from
      Comet Tempel-Tuttle in the year 1333 and they proved for the first time
      that meteoroid streams can have complex braid-like structures within
      them. This work pointed the way to more precise predictions of the
      timing and intensity of meteor showers, such as those Asher and
      McNaught are now making for the Leonids.

      The latest analysis, covering Leonid meteor storms over the past two
      hundred years, shows that the peak times of the strongest storms and
      sharpest outbursts are predictable to within about five minutes. The
      technique involves mapping the fine `braided' structure of the dense
      dust trails within the Leonid meteoroid stream. Although comet
      Tempel-Tuttle, the 'parent' of the Leonid stream, passed close to the
      Earth in 1998, Asher and McNaught predict strong meteor storms in both
      2001 and 2002. 1999 and 2000 will be less spectacular, but good. In
      1999, observers at European longitudes are favoured, and may see up to
      20 meteors a minute (in ideal conditions under a clear, dark sky) at
      around 2 a.m. on the morning of November 18th.

      Meteors, popularly known as 'shooting stars', can be seen on any night,
      given a sufficiently clear, dark sky. They are produced by the impact
      on the Earth's atmosphere of small dust grains released from comets.
      Most meteors arrive in 'showers' at fixed times of the year, when the
      Earth passes close to the orbit of the parent comet. But occasionally -
      just a few times a century - a phenomenon known as a meteor storm
      occurs. During a storm, meteors appear at astonishing rates, sometimes
      several per second. The most famous example, the incredible Leonid
      display of 1833, is credited with starting the serious scientific study
      of meteors.

      Good news for meteor observers can be a concern for satellite
      operators. A satellite can be disabled by the impact of even a small
      dust grain. While the hazard from man-made space debris is well known,
      the danger from meteoroids has been more difficult to assess. Prior
      knowledge of the detailed structure of the Leonid stream is potentially
      of immense value. Satellite operators could use this information to
      take appropriate avoiding action and minimise the risk. With this new
      work, McNaught and Asher have defined the structure of the Leonid dust
      trails more accurately than ever before.


      What are the Leonid meteoroid stream and the Leonid meteor shower?

      The Leonid meteor display is associated with the Earth's passage
      through the Leonid stream. This stream consists of the debris of
      Tempel-Tuttle, a comet that orbits the Sun about every 33 years.

      When do the most intense outbursts occur?

      Although the Earth goes through the Leonid stream every November, in
      most years the Leonid meteor shower is unspectacular. However, there is
      fine structure within the stream, and meteor storms occur when the
      Earth runs through the highest density regions. The new technique for
      mapping out the structure involves precise calculations of the effect
      of the gravity of the planets on the dense dust trails, covering many
      revolutions of the dust grains about the Sun over periods of a century
      or two.

      Why are some longitudes favoured?

      The meteors in any given shower come from a particular direction in
      space. You need to be on the hemisphere facing that direction to see
      the meteors. It also has to be night-time, except for incredibly bright
      fireballs. In the case of the Leonids, an approximate rule is to
      observe after midnight. Background Leonids (a few meteors per hour)
      appear for a few days, and so all parts of the Earth have a chance to
      catch them. But some outbursts are of high intensity for less than an
      hour, and you have to be at a longitude where the time is between
      midnight and dawn. The next few years will provide various excellent
      Leonid opportunities, of which 2001 from East Asian longitudes will be
      best, especially as the moon will be absent from the sky. Most
      immediately, 1999 should produce a good display, although rates will
      not match the most spectacular ones: the Zenithal Hourly Rate (defined
      for an individual observer in near-ideal observing conditions) is
      estimated to peak at 1,200 per hour at 02:08 GMT on November 18th.

      Can damage to satellites occur?

      Very high speed impacts of tiny dust grains on satellites can cause
      plasma to be generated, which can lead to electrical failure. There is
      evidence that the Olympus communications satellite was disabled owing
      to the impact of a meteoroid from the Perseid stream in 1993.

      History of this work

      The famous Leonid storms of 1833, 1866 and 1966 were known to relate to
      the roughly 33 year period of the comet. But it was only when McNaught
      examined the details of those and other Leonid outbursts of the past
      two hundred years that the full predictive power of the 'dust trail'
      technique became apparent. Whereas theories that considered the comet
      alone, rather than the dust trail structure in the stream, would
      sometimes match observed timings of storms within hours (but
      occasionally fail completely), the dust trail theory allows an accuracy
      that many astronomers never suspected possible. Further refinements to
      the theory, including a topographic correction, have reduced the
      uncertainty to around five minutes.

      A few months after developing the technique, McNaught and Asher
      extended their work to permit estimates of meteor rates (in addition to
      predicting storm timings), and applied it to forthcoming encounters of
      the Earth with Leonid dust trails. There is no doubt that 2001 and 2002
      will provide opportunities to witness exceptional Leonid meteor storms.

      The fact that something out of the ordinary is expected in both 2001
      and 2002 had in fact been published more than a decade ago, by two
      researchers, Kondrat'eva and Reznikov, in Kazan, Russia. The English
      translation of their paper did not come to the notice of many western
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