C/1998 P1 Williams
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Comet C/1998 P1 was discovered on 10 August 1998 by Peter Williams (Heathcote, Australia). At the moment of discovery, C/1998 P1 was about 2 months before its perihelion passage and it was last observed in the mid-May 1999.
Comet had its closest approach to the Earth on 28 July 1998 (0.887 au), about 2 weeks before its discovery.
This is a comet with nongravitational effects strongly manifested in positional data fitting.
Solutions given here are based on data spanning over 0.758 yr in a range of heliocentric distances: 1.56 au – 1.15 au (perihelion) – 3.13 au.
This comet suffers large planetary perturbations during its passage through the planetary system; these perturbations lead to a significantly more tight future orbit with semimajor axis of about 830 au. See also Królikowska 2020.

solution description
number of observations 461
data interval 1998 08 11 – 1999 05 15
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 1.56 au – 1.15 au (perihelion) – 3.13 au
detectability of NG effects in the comet's motion comet with NG effects strongly manifested in positional data fitting
type of model of motion GR - gravitational orbit
data weighting YES
number of residuals 912
RMS [arcseconds] 1.46
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 1998 11 03
perihelion date 1998 10 17.85087613 ± 0.00008524
perihelion distance [au] 1.14659254 ± 0.00000088
eccentricity 0.99973479 ± 0.00000335
argument of perihelion [°] 294.483227 ± 0.000095
ascending node [°] 156.375782 ± 0.000074
inclination [°] 145.72946 ± 0.000027
reciprocal semi-major axis [10-6 au-1] 231.30 ± 2.92
Upper panel: Time distribution of positional observations with corresponding heliocentric (red curve) and geocentric (green curve) distance at which they were taken. The horizontal dotted line shows the perihelion distance for a given comet whereas vertical dotted line — the moment of perihelion passage.
Lower panel (panels): O-C diagram for this(two) solution (solutions) given in this database, where residuals in right ascension are shown using magenta dots and in declination by blue open circles.