C/1998 P1 (Williams)

Comet Williams, also known as C/1998 P1, is a non-periodic comet that was observed between August 1998 and April 1999. It is the only comet discovered by Australian astronomer Peter Francis Williams.

C/1998 P1 (Williams)

Comet Williams as imaged by the European Southern Observatory on 11 August 1998[1]
Discovery[2]
Discovered by	Peter Francis Williams
Discovery site	Heathcote, Australia
Discovery date	10 August 1998
Orbital characteristics[3]
Epoch	15 December 1998 (JD 2451162.5)
Observation arc	240 days
Number of observations	403
Aphelion	~3,580 AU
Perihelion	1.146 AU
Semi-major axis	~1,800 AU
Eccentricity	0.99936
Orbital period	~75,700 years
Inclination	145.73°
Longitude of ascending node	156.37°
Argument of periapsis	294.45°
Mean anomaly	0.001°
Last perihelion	17 October 1998
TJupiter	–1.406
Earth MOID	0.410 AU
Jupiter MOID	0.476 AU
Comet total magnitude (M1)	7.8
Comet nuclear magnitude (M2)	14.0

Observational history

While observing the nova EK Trianguli Australis after many days of unfavourable weather,^[4] the comet was visually discovered by Peter Francis Williams while using an 0.3 m (12 in) reflector telescope on the night of 10 August 1998.^[2] At the time, it was a magnitude-9.5 object within the constellation Circinus.^[a] Additional observations by Gordon J. Garradd, David A. J. Seargent,^[2] Steven Lee,^[5] and other astronomers later verified the existence of this comet on two subsequent nights after discovery, albeit at a much fainter magnitude between 13.4 and 16.0.^[5]

Orbit

The comet has a retrograde orbit that is inclined by about 145.73° from the ecliptic. It reached perihelion at a distance of 1.146 AU (171.4 million km) on 17 October 1998. A study of the non-gravitational effects on this comet indicate that it was dynamically new, and its apparition in 1998 were likely its first passage through the inner Solar System.^[6]

Notes

1. Reported initial position upon discovery was: α = 15^h 10.8^m , δ = –64° 59′^[2]