------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 857 1994 July 16 16.25UT 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 ------------------------------------------------------------------- PERIODIC COMET SHOEMAKER-LEVY 9 (1993e)/COLLISION WITH JUPITER Mark Kidger,(TA Planetary Editor),Teide Observatory,Tenerife reports: We are observing Jupiter with narrow-band, methane filters in two telescopes (the 82cm reflector and a German collegue in the 45cm Gregory Solar Tower) and in the infrared with an infrared camera and a 2.2 micron filter in the 1.5m telescope. Prospects for observing tonight are excellent, with clear skies and perfect horizontal visibility, although the solar astronomers report rather poor seeing at present. The first impact will be a few minutes before our local sunset but, with the narrow band filters, we have no problems with CCD observing at that time and can start in some filters 2 hours before sunset, giving us a 5 hour observing run (half a rotation). For the impact we will concentrate on using a filter at 8920 Angstroms, in a deep methane absorption band: this filter shows us a layer of the atmosphere well above the cloud tops seen in visible light and is the best one for showing possible impact activity. Whether or not we will see anything is another question. Note that fragment W (whose impact can be seen from Europe/Africa) and fragment V, which will impact long after Jupiter has set in the Canaries, but will be visible in America, are very small indeed. The latest results (HST) suggest the smaller fragments being under 100m diameter. Brian Marsden warns that, until Monday, we are not likely to see anything AT ALL. Remember that the first impacts take 15 minutes to reach the limb and then some 10 minutes more to get into daylight (there is a significant phase effect). Even so, do not expect to see activity close to the limb. The high aerosol layer will obscure any but the very highest cloud layers until they are well into the disk. In the HYPOTHETICAL case that something were to be seen tonight, the signature would be a very small, bright cloud that would be at very high level and would probably show up rather close to the limb. Note that the 1990 Great White Spot of Saturn was only visible initially when less than 38 degrees from the central meridian. If this were the case for Jupiter, we might have to wait well over an hour for any structure to get far enough into the disk to be seen. Note too that the region to the south of the GRS has a lot of white spot activity. Observing tonight's impact site two nights ago we saw a chain of white spots near the impact position. There were four in total, with a steady reduction in size from first to last. The latitude is somewhat north of the impact position, but these spots may fool some observers. The first two have longitude 158 and 171 degrees (System II), with approximately equal separations to the following two. The latitude is -30 deg. Note that the first impact should be at long=177, lat=-44, south of, but right in the middle of the spots. The impact of the biggest fragment (7a=Q1) on Wed. night, will be quite close to, but south of the GRS. Guy M Hurst --- 00015 --- Subject: Impact