C/1999 U1 Ferris
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C/1999 U1 was discovered on 18 October 1999 by W.D. Ferris of LONEOS team [IAUC 7283, 1999 October 18]. Later, pre-discovery measurements taken by Siding Spring on 22 December 1998 were found.
This comet made its closest approach to the Earth on 11 December 1998 (3.667 au), 3.3 months after perihelion.
Solution given here is based on data spanning over 1.1 yr in a range of heliocentric distances from 4.24 au to 5.89 au.
This Oort spike comet suffers rather strong planetary perturbations during its passage through the planetary system that lead to notable more tight future orbit with semimajor axis shorter than 2000 au (see future barycentric orbit).
See also Królikowska 2014 and Królikowska and Dybczyński 2017.

solution description
number of observations 208
data interval 1998 12 22 – 2000 01 28
data type observed only after perihelion (POST)
data arc selection entire data set (STD)
range of heliocentric distances 4.24 au – 5.89au
detectability of NG effects in the comet's motion NG effects not determinable
type of model of motion GR - gravitational orbit
data weighting YES
number of residuals 410
RMS [arcseconds] 0.51
orbit quality class 1a
orbital elements (heliocentric ecliptic J2000)
Epoch 1998 08 15
perihelion date 1998 09 03.02800700 ± 0.00349400
perihelion distance [au] 4.13756580 ± 0.00002406
eccentricity 1.00365011 ± 0.00001242
argument of perihelion [°] 291.063317 ± 0.000628
ascending node [°] 58.257256 ± 0.000024
inclination [°] 105.73481 ± 0.000121
recip semi-major axis [10-6 au-1] -882.19 ± 2.99
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