C/1978 A1 West
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Comet C/1978 A1 was discovered on 12 January 1978, almost six months after its perihelion passage, and was last seen on 7 April 1978 [Kronk and Meyer, Cometography: Volume 5]; later few prediscovery measurements going back up to 30 March 1976 were found, that is 15.5 months before its perihelion passage (see figure).
The comet made its closest approach to the Earth on 8 May 1977 (4.71 au), that was seven months before its discovery; however, in its next opposition – three months after discovery – the comet approached minimal distance of 4.94 au from the Earth (on 10 April 1978).
Solution given here is based on data spanning over 3.24 yr in a range of heliocentric distances: 6.57 au – 5.61 au (perihelion) – 7.50 au.
This Oort spike comet suffers small planetary perturbations during its passage through the planetary system that lead to escape the comet from the planetary zone on a hyperbolic orbit (see future barycentric orbit).
See also Królikowska 2014 and Królikowska and Dybczyński 2017.

solution description
number of observations 62
data interval 1976 03 30 – 1979 06 26
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 6.57 au – 5.61 au (perihelion) – 7.5 au
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 120
RMS [arcseconds] 1.30
orbit quality class 1a
orbital elements (heliocentric ecliptic J2000)
Epoch 1977 08 05
perihelion date 1977 07 21.55515600 ± 0.00668500
perihelion distance [au] 5.60632765 ± 0.00003869
eccentricity 1.00294290 ± 0.00006749
argument of perihelion [°] 343.283932 ± 0.000542
ascending node [°] 211.623628 ± 0.000070
inclination [°] 116.930129 ± 0.000162
recip semi-major axis [10-6 au-1] -524.92 ± 12.03
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