Satgen502  Comets and Meteors Pt1 by GM4IHJ (BID SGEN502)   1998-11-07

On Tuesday 17th November next, we may see a first class meteor shower.
Past examination of the orbit and timing of this shower , indicates
that it is produced when the Earths orbit around the Sun takes us
through the debris stream cast out by Comet Temple-Tuttle. 20 year ago
none of this was obvious. The connection between annual meteor showers
and comet orbits was debated but not proven. But that situation
changed when the IRAS Infra Red satellite began to look into space,

IRAS revealed the existence of Infra red stars, as expected. But
unexpectedly, it showed what looked like long aircraft vapour trails
in space. Trails where something was radiating infra red, along lines
up to a million miles long. Indicating the presence of something warm
enough to be clearly seen in infra red light. Trails of small
particulate debris along almost straight lines going both in and out
of the solar system. Specialists in orbital mechanics calculated the
orbits of the track materials, and found that one of them coincided
with the orbit of a small dead asteroid which had long been associated
withe Geminid meteor shower of December. Connections with other
"comets" or, asteroids which had once been comets were soon
established.

To date the connection between a particular comet and its meteor
stream , has been established for the following meteor showers :-

    Shower       Month        Comet
    Lyrids       April        Comet 1861 I
    Acquarids    May          Halley ( outgoing )
    B Taurids    June         Encke
    Draconids    June         Pons-Winnecke
    Perseids     August       Swift-Tuttle / Kegler
    Draconids    October      Giacobini-Zinner
    Orionids     October      Halley ( incoming )
    E Taurids    November     Encke
    Leonids      November     Temple-Tuttle
    Andromids    November     Biela (comet appears to have broken up)
    Geminids     December     Dead Asteroid former comet ?
    Ursids       December     Tuttle 1939X

We are normally only concerned with these comet debris trails where
they cross the Earths orbit . Not all comets come in on a plane near
that of the earths orbit . Those which do , like Comet Halley produce
debris streams the Earth collides with twice a year . Many other
comets come in and out round the Sun on highly inclined orbits such
that the earth only encounters them once , or in some cases does not
encounter them at all. The material escaping from the comet , leaves
it with only a very slight difference in velocity from that possesed
by the comet itself. None the less in the course of hundreds of years
this material orbits with the comet gradually spreading all around the
orbit track . This spread does not occur evenly. Some Earth encounters
produce lots of meteors, whilst others do not. Other planets also
encounter the debris stream  from time to time, further dispersing or
reducing its contents.