Sun Jul 24 17:19:07 1994
The length of the following message is not intended to set a precedent, but as several people have asked about the present visible evolution of the impact sites, here is an update, plus a note of thanks to you all.
(1) LATEST VISUAL OBSERVATIONS, July 22 and 23. (Longitudes are tabulated below.) July 22 (20h-22h): James Lancashire (JAL) and Paul Doherty (PD), both using 30-cm telescopes. Site C: Still present after 5 days without substantial fading. Site K/U/W: The overall appearance has not changed much since July 20 but it now contains 3 (JAL) or 4 (PD) dark nuclei. Site L: Still large and dark. July 23 (19.30-21.30): John Rogers, 30-cm refractor. The appearance is just amazing - the planet really has been thoroughly carpet-bombed. Site L: Still large and dark after 4 days, broken into several components. Site D/G/S: Large and complex, perhaps the most impressive yet seen. As it approached the p. limb, there was a bright spot on the limb Np. it. Site R: A tiny black spot south of the main line of dark spots, close to D/G/S with a tiny bright spot between. (R and Q1 were identified from the longitudes given by the Hubble team; see below). Site Q1: A single black spot like a satellite shadow. Cannot see site N. Site H: Remarkable changes now it is 5 days old. It is a very dark spot, obviously north of the main line, but may have a black Sf. tip which would be on the line. Also, there was a light area f. it when coming in from the f. limb, and a bright spot p. it when on the disk.
In general, the large spots have remained prominent for up to 5 days, but are distorting, as if stratospheric currents are carrying the 'smoke' to E. or N. or S.
There are several indications that light material may be spreading through the region. We have to beware of visual contrast effects but what I see are:
Given the small size of sites R and Q1 (and the difficulty of disentangling S and W from previous sites), it appears possible that the comet had 3 classes of sub-nuclei: (i) those displaced tailward, whose impacts were not detectable (or barely so); (ii) the early 'on-line' nuclei, which produced prolonged fireballs and large scars, in proportion to their brightness in the comet; (iii) these later on-line nuclei, which produced briefer fireballs and smaller scars.
(2) PRESENT LIST OF VISIBLE SCARS
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Site \3 \3 \2 Date
(HST) (vis) (vis)
---- ----- ----------- ------------ -------
A 185 178 107 July 19** (faint)
C 224 219 148 July 19**
K/W - 263-278-283 191-206-211 July 22** (JAL)
L - (mid.342) (mid.270) July 22 (lo-res; JAL)
330-348-352 260-277-281 July 20**
D/G/S 25 (G) (6)-28-31 (293)-315-318 July 23**
R 42 40.5 328 July 23
Q1 64 67 355 July 23
H 101 97 25 July 23
F? - -
E 154 155 83 July 19**
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The second column gives the System III longitudes reported by the Hubble team (as of July 23, presumably from early images). The third and fourth columns give our most recent longitudes, in Systems III and II, from visual obs'ns on the dates given (p.m.). These are by myself except for those marked JAL. Where one value is given, the scar looked like a satellite shadow (except for A); where three are given, they are the p. end, the black core, and the f. end. Values in brackets are approximate.
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(3) THANKYOU BUT NOT GOODBYE
As the dust begins to settle, I really want to say thankyou to everyone who has been involved in disseminating the information about this event. Thanks particularly to Paul Chodas and Don Yeomans for producing all those predictions; to Anne Raugh and Lucy McFadden for operating this exploder service; to Glenn Orton for the International Jupiter Watch (Atmospheres) bulletins prior to the impacts; to anyone else involved whose role I have overlooked; and to EVERYONE who has sent messages about your observations and ideas. Your messages are being summarised as quickly as possible for circulars to amateur astronomers, who will certainly carry on observing. This has been the most exciting (and sleep-deprived) week that I can remember.
It has really been impressive how much everyone has achieved. The press and public must be impressed too: that astronomers can get spectacular predictions right (for once!); that observatories and spacecraft have performed so well (especially Hubble S.T.); and that astronomers worked together so well, and got such splendid data and images out so quickly. The public image of science must have got a real boost from this.
Regarding the visual spectacle, I concur with Clark Chapman that the big impact scars are the most prominent transient spots ever seen on Jupiter, and are easy for anyone with an 8-cm telescope or bigger. ('Transient' excludes the GRS which, we must admit, was stunning around 1880 if not 1990.) Certainly, as Tom Hockey's list shows, such a thing has never happened before in recorded history. (I can say so having reviewed all historical observations as part of the work for my comprehensive book, 'The Giant Planet Jupiter', which is being published by CUP in spring, 1995 - excuse me for slipping that in...)
The show is not over; amateurs will track these scars as long as possible (and keep an eye open for meteors on the limb). I'll be happy to send periodic reports through the exploder - and to receive updates from everyone else - for as long as Anne and Lucy think it's worth operating. Best wishes:
John Rogers (British Astronomical Association). ****************************************************