Satgen 207   The Perseids Meteors - August 93  by GM4IHJ       13th Mar 93
The BIB of this msg is SGEN207 Please use that BID if u retransmit the msg

The Perseids meteor shower produced a few puzzles in the 1980's, when it
was very poor, and, its parent comet failed to appear as predicted. Then
in 1991 the August Perseids were a good radio shower over Europe and a
good visual shower over Japan. A situation which caused the Comet trackers
to look again for Swift Tuttle the parent comet. But nothing was seen, and
when August 92 duly arrived , only optimistic and alerted radio observers
witnessed a very strong shower. So now doubly warned the Comet trackers
got busy and were quickly rewarded when in Sept 92 , Comet Swift Tuttle
was sighted as in headed inbound for perihelion passage round the Sun.
All this watching quickly produced a new set of orbit data for Swift
Tuttle ( last seen way back in 1862 ), and extrapolation forward of this
orbit seemed to suggest that next time Swift Tuttle comes around in July
2126 it may pass near to the Earth. The media naturally rewrote this might
come near to " will probably collide", but as Swift Tuttle now heads away
in March 93 a collision looks even less likely than it did 6 months ago.
So can we all relax ?
Perhaps not. For whilst a direct collision is highly unlikely, a near by
pass is not. At which point readers will recall that we are reasonably
well protected ourselves by the Earth's thick atmosphere. So why worry ?
We should perhaps worry a litle because roughly 25,000 million pounds
sterling's worth of geosats and high elevation navsats and comsats, have
gone up since the last close pass of a comet, and they are not protected
by the atmosphere. Indeed , as Comet probe Giotto showed when it sneaked
past Comet Halley at about 300 kms range , just one hit by comet debris
can be highly damaging . As illustrated by Giotto's heavily protected
hooded and screened camera which took a direct hit and has not worked
since. So what price do we lay on the survival of Astras- Eutelsats
-Marisats- Intelsats-Arabsats etc if a large meteor shower grazes the
earth as the result of a near pass by a comet. We may not need to wait
until 2126 AD to find out. We are due for a regular massive repeat of the
shower which gave birth to the song "Stars Fell in Alhabama". The great
Leonids shower has a rough sequence of 33 year repeats and the next is due
in Nov 98 or Nov 99.
Meanwhile what can we expect from this years Perseids. The 1993 shower
should peak at 0100 ut ( 0200 Bst) on 12th August 93. Given the recent
departure of Swift Tuttle it could perhaps be a shower to remember. For a
couple of hours around maximum its radiant elevation is near the 45 deg
high efficiency point to the north east of UK. So alerted radio amateur
meteor shower communicators should get excellent results into middle,
southern and western Europe from Greece to Spain.
For Radio Experimenters and SWLs counting meteor pings there are several
points worth stressing. 1. Optimum results occur when your antenna is
directed at least 45 degs away from the shower radiant ( see RSGB Space HB
for map). 2. In 92 auto counting using NB CW Rx was hopeless because pings
were too numerous and overlapped. Use Wide band reception to reduce ping
numbers for a clear expression of maximum. 3 Avoid FM stations . They
group 5 at a time on same frequency and blur the count. 4. Last but not
least please note FM or TV may be good targets before midnight but most go
off at local midnight so you could start fine but lose your target station
before shower maximum.  73 de GM4IHJ @ GB7SAN