Satgen 611  Space Dust  by GM4IHJ  ( BIB SGEN611 )    2000-12-09

This coming weekend 11/13 December will see in the peak of the
regular pre Christmas Geminids meteor shower. A shower now believed
to be caused by the dust streams left in the wake of an extinct
comets many perihelion passages around the Sun. The asteroid Phaeton
which follows the self same orbital track as the Geminids may be the
surviving hard core of the original comet , now devoid of loose ice
and dust.

The Geminids are best seen in the evening , when their arrival over
the night side of earth ie a slow pursuit trajectory, gives them a
low relative velocity and hence slow easy to see passage across the
sky. Unlike, the " blink and you miss them", high speed passages of
most meteors. In the eastern evening sky the Geminids come in low on
the horizon from the north and slowly cross to exit south of east. 
So while not as numerous as the January 4th Quadrantids or the August
Perseids, they can be a much better spectacle. Unfortunately the
presence of the Moon in that part of the sky, this week,  may reduce
the quality of viewing of this years display.

The presence of the Moon will not however spoil the radio meteor
scatter possibilities. Nor will it inhibit the random meteor scatter
which several radio amateurs are discovering can make any day ,morning
operating  0600 to 0900 local , very rewarding. The point being that
the morning side of earth, leads as the earth orbits the Sun. So it
collects far more meteor dust ( lower relative velocity ), than other
parts of the earth. Some mornings are better than others , perhaps
around June and December when the earth is passsing through the
ecliptic plane, where the comet trappers Jupiter and Saturn route
most short period comets , and hence where most of the dust collects.
Such that in an average day the earth collects about 40 tons of the
dusty debris, mostly from comets although some clearly comes from
bits knocked off colliding asteroids.

Once or twice a day perhaps , the meteor trail echo returns produce
rapidly curving ie high doppler shift trails as material travelling
much faster than usual, hits the atmosphere. Crude calculations
suggest some of this stuff is impacting at a high enough velocity to
produce a momentary doppler shift of 30 to 50 Hz/sec on a 48 MHz
signal, recorded on an FFTDSP display of signal spectrum whilst
monitoring a low VHF band TV signal. Which might possibly be
announcing the arrival of star stuff - material from outside the
solar system.

Much more convincing than this , is the report of observations made
at the University of Canterbury in New Zealand . Where meteor radar
derived orbit data suggests, that the star source of some of these
high speed arrivals appears to be the star Beta Pictoris. A nearby
star known to be surrounded by a massive disc of dust, B Pictoris is
about 79 Light years from the Sun , visible only from near equatorial
or southern hemisphere stations. It has been suggested, that its dust
ring may conceal newly forming planets.