After a year of anticipation, Periodic Comet Shoemaker Levy 9 is about to put on a grand show, and the world's astronomers are watching. The comet's 20 known fragments will strike the southern hemisphere of Jupiter on the dark side just out of view of Earth, beginning July 16th. The following times are calculated from positional data gathered through July 11th, with a July 15th adjustment for fragment A; a more detailed update is expected just a few hours before the first impact. The values include the 42.5 minutes of light time between Jupiter and the Earth and are given in Pacific Daylight time. However, positional uncertainties are still fairly large, and these times are only good to plus or minus 15 minutes in most cases.
Fragment Date PDT A July 16 1:00 p.m. B 7:54 p.m. C 11:59 p.m. D July 17 4:45 a.m. E 8:05 a.m. F 5:27 p.m. G July 18 12:28 a.m. H 12:26 p.m. K July 19 3:18 a.m. L 3:07 p.m. N July 20 3:21 a.m. P2 8:10 a.m. Q2 12:32 p.m. Q1 12:59 p.m. R 10:24 p.m. S July 21 8:10 a.m. T 11:06 a.m. U 2:53 p.m. V 9:15 p.m. W July 22 12:57 a.m.< The impacts of fragments B, F, R, and V are the only ones that occur when Jupiter is viewable from North America. Even though the impacts themselves occur on Jupiter's back side, the target zones will rotate into view along the planet's southeast limb no more than 20 minutes later.
Unfortunately Jupiter will be observable well for only an hour or two out of every 24 from any given location at north temperate latitudes. It's the bright "star" fairly high in the southwest as darkness falls. The cover story of the July Sky & Telescope provides full coverage of this event and how to try to watch.
A new analysis of Hubble Space Telescope images suggests that the impacts could be impressive. Zdenek Sekanina reports that not only do the biggest nuclei appear to be 3 to 4 kilometers across, but some of them may have split off smaller clumps as they have neared the planet.
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