C/1916 G1 Wolf
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Comet C/1916 G1 was discovered on 4 April 1916 by Max F.J.C. Wolf (Königstuhl Observatory, Heidelberg, Germany), that is about 14.5 months before its perihelion passage, and the comet was last seen on 29 January 1918 [Kronk, Cometography: Volume 3].
This comet made its closest approach to the Earth on 21 August 1917 (0.988 au), that is about two months after its perihelion passage.
Solutions given here are based on data spanning over 1.81 yr in a range of heliocentric distances from 5.16 au through perihelion (1.69 au) to 3.25 au.
Pure gravitational orbit determined from all available positional measurements (469 observations) give 1a-class orbit, orbit given in Minor Planet Center is 2A class (186 obs. used, almost the same arc of data; see MPC).
It was possible to determine the non-gravitational orbit for C/1916 G1 (preffered orbit), the RMS for NG orbit decreases from 1.97 arcsec (pure gravitational orbit) to 1.84 arcs.
This Oort spike comet suffers moderate planetary perturbations during its passage through the planetary system that lead to a more tight future orbit with semimajor axis of about 1300 au (see future barycentric orbits given here for both solutions: pure gravitational and non-gravitational).
More details in Królikowska et al. 2014.

solution description
number of observations 471
data interval 1916 04 07 – 1918 01 29
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 5.16 au – 1.69 au (perihelion) – 5.74 au
type of model of motion NS - non-gravitational orbits for standard g(r)
data weighting YES
number of residuals 817
RMS [arcseconds] 1.84
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 1917 06 21
perihelion date 1917 06 17.07437692 ± 0.00027414
perihelion distance [au] 1.68642132 ± 0.00000382
eccentricity 0.99932117 ± 0.00000954
argument of perihelion [°] 120.621627 ± 0.000182
ascending node [°] 184.457166 ± 0.000054
inclination [°] 25.658821 ± 0.000063
recip semi-major axis [10-6 au-1] 402.53 ± 5.66
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
non-gravitational parameters
A1 [10-8au\day-2] 2.502 ± 0.442
A2 [10-8au\day-2] 0.708 ± 0.363
A3 [10-8au\day-2] -0.2692 ± 0.0699
m -2.15
n 5.093
k -4.6142
r0 [au] 2.808
α 0.1113