Mon Jul 25 01:15:50 1994

The status of the dark spots in the week after the impacts

Following extensive visual studies of all major dark spots on Jupiter with a 16-inch Cassegrain on Cerro Tololo Interamerican Observatory, here is a summary of what the inidividual regions looked like to the eye (no filters available) under ideal conditions on the nights 22/23 and 23/24 and under deteriorating seeing on the evening of July 24th. Emphasis is on the areas where something happened and not so much on the fate of each individual fragment; sometimes it's not clear anyway which part of a region relates to which impact. The listing is in alphabetical order = time sequence of the major impacts; at this time all the 'regions' addressed are clearly distinct.

The "Visibility Index" is a spontaneously invented measure for how easy a region is to see (and thus of the minimum telescope size required): Index I is so striking that even a 60 mm spotting scope (of sufficient magnifica= tion) should not fail to show it, II is harder but should be easy in any decent amateur telescope, III may require a more advanced scope and/or good seeing as the lack of a dark Core gives these regions much lower contrast.

A (after 7 days): A pretty faint elongated mass of dark material, oriented in
    a more or less North-South direction, connected (?) to the STrB. No dark
    nucleus visible. Visbility Index III

C (after 6 days): A grey mass, extended both in NS and EW direction. No dark
    nucleus evident. (A distinct White Oval Spot is in the STrB north of it!
    The surrounding belt is significantly darker.) Visibility Index II-III

E (after 6 days): Consists of a dark Core (Visibility Index I) and an extended
    winglike halo, with two spikes pointing towards the West, the more
    northern one is connected to the STrB. Whole Structure: Vis. Ind. I-II

G (after 5+7 days): By far the most impressive feature, no aging whatsoever
    visible over three days! The dark Core is extremely long (and connected to
    the much smaller but very dark R site), to the south is an extended Halo,
    almost as dark. The structure looks like a squirrel :-) Its extent in
    longitude was measured to roughly 30 000 km. Visibility Index I

H (after 4 days): Probably the most bizarre impact site. There is a dark Core,
    but from it emanate long wisps of dark material to both the SW and N.
    Visibility Index I. (After 6 days): Structure resembles a smoking volcano,
    sitting on the STrB, with 'smoke' extending to the WSW. Vis. Ind. I-II

K (after 4+5 days): The secondmost impressive impact region after G, looks more
    like a sunspot group than any other. There's a very long (25-30 000 km)
    'penumbra' in EW direction, inhabited by two big dark 'umbrae', while
    yet another 'umbra' accompanies these spots to the south. Vis. Ind. I

L (after 3+4+5 days): Another quite bizarre region, with several dark Cores
    and halo structures, extending along a SE - NW axis. Visibility Ind. I

Q (after 2 days): Mainly a dark Core (Vis. Ind. I-II) with a Halo (V.I. II-III).
    (After 4 days): Another, even smaller spot (Vis. Ind. II-III) precedes Q

General Impression: All Regions of Visibilty Indices I and II are much darker than anything else on the planet except the occasional satellite shadow in transit; if you want to see the most awesome view I recommend times when G, L and K are all on the visible hemisphere [such as on July 23rd at 23:30 UTC]. No image in the visible that has been distributed on the network, by the way, has *really* captured the awesome size, darkness and wealth of detail of the major impact areas - not even the recent images from the Space Telescope (where the 'normal' cloud features appear too prominent in comparision with the direct view the eye has, thus dimimishing the startling difference in contrast between the spots and the normal meteorology of Jupiter). Only HST's monochromatic view in the UV of several sites comes closer to the actual view.

The drawings obtained at the CTIO 16" will be presented at the 2nd Meeting of European Planetary and Cometary Observers (MEPCO'95) in Violau, Germany, March 24-27, 1995 where Gene Shoemaker will be the keynote speaker and the face of Jupiter after the demise of SL9 should be the major topic. A collection will also be submitted to the J.A.L.P.O. and is also due to appear in the next edition of the newsletter Skyweek, available from the undersigned.

Daniel Fischer, leaving Cerro Tololo today and heading back to Germany soon ->
   Im Kottsiefen 10, 53639 Koenigswinter, FRG; p515dfi@fs1.mpifr-bonn.mpg.de