C/1998 P1 (Williams)

Lore & Background

Comet Williams was visually discovered by Peter Francis Williams on the night of 10 August 1998, while he was observing the nova EK Trianguli Australis after many days of unfavourable weather. He used a 0.3 m (12 in) reflector telescope, and at the time the comet was a magnitude-9.5 object within the constellation Circinus. Its existence was later verified on two subsequent nights by Gordon J. Garradd, David A. J. Seargent, Steven Lee, and other astronomers, though it appeared much fainter, between magnitudes 13.4 and 16.0.

Orbital calculations indicate the comet is non-periodic, with a retrograde orbit inclined about 145.73° from the ecliptic. It reached perihelion at a distance of 1.146 AU on 17 October 1998. A study of non-gravitational effects suggests the comet was dynamically new, and its 1998 apparition was likely its first passage through the inner Solar System. An apparent outburst in September 1998 increased its brightness to magnitude 7.4. The comet's brightness remained consistent on its outbound trajectory: Alan Hale reported magnitude 9.4 in November 1998, and it slightly brightened to magnitude 9.0 in December 1998 and magnitude 9.2 in February 1999.

Reader's Guide

Comet Williams is significant as the only comet discovered by Australian astronomer Peter F. Williams, and its discovery occurred during an observation of the nova EK Trianguli Australis. The comet's orbital characteristics, including its retrograde orbit and high inclination, mark it as a dynamically new object that likely entered the inner Solar System for the first time in 1998. Its brightness varied notably, with an outburst in September 1998 raising it to magnitude 7.4, followed by a gradual fading and slight brightening over subsequent months. The comet's non-periodic nature and orbital projections indicate an 80% probability that it will be ejected from the Solar System on its next few perihelion passages or apparitions. This makes Comet Williams a valuable object for studying the behavior of dynamically new comets and their potential ejection from the Solar System.

Did You Know?

• It was discovered visually using a 0.3 m (12 in) reflector telescope on 10 August 1998.
• The comet's orbit is retrograde and inclined 145.73° from the ecliptic.