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THE ASTRONOMER Electronic Circular No 858      1994 July 17 17.55UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074
INTERNET: GMH at AST.STAR.RL.AC.UK  or    GMH at GXVG.AST.CAM.AC.UK
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PERIODIC COMET SHOEMAKER-LEVY 9 (1993e)/COLLISION WITH JUPITER
Mark Kidger, Teide Observatory reports:
Detection with Spanish telescopes of the impact of Comet (1993e).
At 20:18UT on 1994 July 16 a spot was detected on Jupiter in the
position corresponding to the impact site of the first fragment of
the comet (Nucleus A or 21). This observation was made by
astronomers at the Instituto de Astrofisica de Canarias (IAC) with
the 1.5m Carlos Sanchez, infrared telescope and with the 82cm
IAC-80 Telescope, both in Teide Observatory (Tenerife); a
near-simultaneous detection was made by IAC astronomers,
collaborating with a French group from the Service d'Astrophysique
(CEA) in the 2.56m Nordic Optical Telescope at El Roque de los
Muchachos Observatory (La Palma). The detection was first made in
the infrared and then, later, in the visible. According to the
Central Bureau for Astronomical Telegrams of the IAU, this was the
first report received of a detection of the impact from anywhere
in the world.
The spot was extraordinarily bright, slightly less than the
satellite Io in the infrared and was between 20 and 30 thousand
kilometres in length, rather larger than the Great Red Spot.
The bright spot was very short lived: after 15 minutes, two of the
three telescopes had virtually lost it from view. However, two
hours later, a very faint cloud was still visible, a remnant of the
explosion. This spot moved across the disk much more slowly than
the visible cloud features, demonstrating that it is in the
stratosphere of the planet, well above the visible clouds.
Despite careful observation of Jupiter with optical telescopes
(the 82cm IAC-80 Telescope and the 45cm Gregory Solar Tower: both
in Teide Observatory, Tenerife) and telescopes in South Africa,
the cloud was not seen clearly until some two and a half hours
later. The observations appear to suggest that a bubble of hot gas
formed above the impact site, but that the gas was not hot enough
to emit significantly in the visible, emitting mainly in the
infrared range. Shortly after appearing, the gas cooled and ceased
emitting strongly in the infrared. The faint spot that has been
seen since appears to be a cloud that has formed at very high
altitude. the delay in the movement of the spot with respect to
the Great Red Spot which was simultaneously visible in the disk
indicates that the rotation of the upper atmosphere of Jupiter is
very slow compared to the lower levels. Without doubt, the
observations, which will now have to be analysed in great detail,
are going to provide a lot of headaches for scientists who study
them. The success of the observations and the possible detection in
Japan of a radio event corresponding to the impact of a small
fragment two days ago (this fragment would have been well outside
the main body of the comet) suggests that, although the visible
detection of the impacts will be very difficult, the infrared
telescopes are going to view an ever more impressive spectacle,
especially when the impacts of the largest fragments take place
next Monday and Wednesday.

Guy M Hurst







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Date: 18 Jul 1994 12:20:09-BST