C/1948 T1 Wirtanen
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Comet C/1948 T1 was discovered on 7 October 1948, about 13 months after perihelion passage and was last seen on 11 September 1950 [Kronk, Cometography: Volume 4].
This comet made its closest approach to the Earth on 26 October 1947 (2.44 au), that is one month after perihelion passage and almost one year before its discovery.
Solution given here is based on data spanning over 1.86 yr on postperihelion leg of orbit in a range of heliocentric distances from 4.89 au to 9.38 au.
This Oort spike comet suffered small planetary perturbations during its passage through the planetary zone that caused a bit tighter future orbit (see original and future barycentric orbits).
More details in Królikowska et al. 2014 andKrólikowska and Dybczyński 2017.

solution description
number of observations 26
data interval 1948 10 07 – 1950 08 17
data type observed only after perihelion (POST)
data arc selection entire data set (STD)
range of heliocentric distances 4.89 au – 9.38au
detectability of NG effects in the comet's motion NG effects not determinable
type of model of motion GR - gravitational orbit
data weighting NO
number of residuals 52
RMS [arcseconds] 0.94
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 1947 09 12
perihelion date 1947 09 04.42951500 ± 0.01032300
perihelion distance [au] 3.26110877 ± 0.00011350
eccentricity 1.00227683 ± 0.00003289
argument of perihelion [°] 73.464822 ± 0.001866
ascending node [°] 122.120668 ± 0.000217
inclination [°] 155.077948 ± 0.000265
reciprocal semi-major axis [10-6 au-1] -698.18 ± 10.07
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.