Astronomical naming conventions order of their discovery. Thus Bennett's comet has the systematic designation C/1969 Y1. Halley's Comet, the first comet to be identified as periodic, has the systematic name 1P/1682 Q1. Comet Hale–Bopp's systematic name is C/1995 O1. The famous Comet Shoemaker–Levy 9 was the ninth periodic comet jointly discovered by Carolyn Shoemaker, Eugene Shoemaker, and David Levy (the Shoemaker–Levy team has also discovered four non-periodic comets interspersed with the periodic ones), but its systematic name is D/1993 F2 (it was discovered in 1993 and the prefix "D/" is applied, because it was observed to crash into Jupiter). Some comets were first
Comet Shoemaker–Levy 9 Despite published predictions, astronomers had not expected to see the fireballs from the impacts and did not have any idea in advance how visible the other atmospheric effects of the impacts would be from Earth. Observers soon saw a huge dark spot after the first impact. The spot was visible even in very small telescopes, and was about (one Earth radius) across. This and subsequent dark spots were thought to have been caused by debris from the impacts, and were markedly asymmetric, forming crescent shapes in front of the direction of impact. Over the next six days, 21 distinct impacts