Satgen585  A New Comet ?  by GM4IHJ  (BID SGEN585)    2000-06-10

Most of the comets we see in our skies have been around the Sun many
times . Confined in short period orbits. They appear regularly every
few years. Never going further out from the Sun than the orbit of the
planet whose gravity constrained them when they passed close to it on
their long ago first trip into the inner solar system. These regular
visitors make hundreds of short duration orbits past the Sun,
gradually losing all their outer ice and dust. Until, reduced to an
almost invisible small rocky core or cinder, they circle unseen by
all but the big telescopes. Identified , as former comets perhaps ,
only if, as in the case of one well known comet/asteroid they follow
the same orbit as the regular annual December Geminids meteor shower.

Other longer period comets like Halley, have been trapped by one of
the outer planets . Confining them to orbits of 70 to 1000 years
duration. They still have plenty of ice and dust left, which produces
beautiful shiny tails as it glistens in sunlight as they come in past
the earth on these less frequent visits. 

Much rarer, are the "New Comets". Comets coming into the solar system
for the first time,if they are not captured by passing close to
one of the planets, may simply go around the Sun and straight out
again, never to return. On their way in they have a very bright
appearance even when far from the Sun. But this can be deceptive,
being caused by a very light covering of loose icy material which is
soon lost. After which they continue into the inner solar system
sometimes stubbornly refusing to get any brighter. A feature which
has in the past caused a great deal of disappointment.  

Comet Linear was first spotted by the Lincoln laboratory Near Earth
Asteroid Reseach survey in September 99. By July 2000 it will pass
across the Northern sky just under the Big Dipper in the
constellation of Ursa Major . But will this newcomer be bright enough
to be seen without a big telescope ? 

It just might. But recent observations as it gets closer to the inner
solar system suggest caution. As it got closer, the collection and
measurement of its orbital parameters has improved, and these suggest
that it is indeed a brand new comet with an orbital eccentricity of
slightly more than 1. So its orbit is not a closed conic section , it
is hyperbolic ,probably on its first and last visit before it heads
off out of the solar system. In consequence of which , its intial
brightness as it passed Jupiter may be misleading. It may never be a
bright visual object. 

It will certainly be visible to telescope viewers and probably also
to users of modest binoculars. But its timing as a summer northern
sky object is not going to help. In Scotland and other locations
above 56 north latitude, the lack of absolute darkness at this time
of year, will mean poor viewing conditions. Whereas South African
observers may get quite a good view of Comet Linear in August as it
crosses their clear evening skies. Then just maybe, a million years
after leaving the solar system, it may brighten the skies of a
planet of a star far from earth.