C/1919 Q2 Metcalf
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Comet C/1919 Q2 was discovered on 23 August 1919 by Joel Hastings Metcalf (Camp Idlewild, South Hero, Vermont, USA), that is about 3.5 months before its perihelion passage, and the comet was last seen on 17 February 1920 [Kronk, Cometography: Volume 3].
This comet made its closest approach to the Earth on 29 November 1919 (1.90 au), that is eight days before its perihelion passage.
Solution given here is based on data spanning over 0.444 yr in a range of heliocentric distances from 1.951 au through perihelion (1.115 au) to 1.446 au.
This Oort spike comet suffers very slight planetary perturbations during its passage through the planetary system; however, they lead to escape the comet from the planetary zone on a hyperbolic orbit (see future barycentric orbit).
More details in Królikowska et al. 2014.

solution description
number of observations 276
data interval 1919 08 25 – 1920 02 03
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 1.95 au – 1.11 au (perihelion) – 1.75 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 498
RMS [arcseconds] 2.58
orbit quality class 2a
orbital elements (heliocentric ecliptic J2000)
Epoch 1919 11 18
perihelion date 1919 12 07.80964754 ± 0.00209604
perihelion distance [au] 1.11527223 ± 0.00002732
eccentricity 1.00020566 ± 0.00007480
argument of perihelion [°] 185.753567 ± 0.002470
ascending node [°] 122.098062 ± 0.000560
inclination [°] 46.38187 ± 0.000174
recip semi-major axis [10-6 au-1] -184.40 ± 67.07
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