C/1978 A1 West

Solar System
Dynamics &
Planetology
Group

C/1978 A1 West

General description

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 approach minimal distance of 4.94 au from the Earth (on 10 April 1978).

Solution given below is based on data span over 3.24 yr in the range of heliocentric distances: 6.57 au – 5.61 au (perihelion) – 7.50 au.

Figure caption: 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.

SSDP Cometary Note C1978A1A1-001

Comet C/1978 A1 West

number of observations	62
number of residuals	120
data interval	1976 Mar. 30 — 1979 June 26
rms [arcsec]	1.30
orbit quality class	1a

Osculating orbital elements (heliocentric; ecliptic J2000.0)

Epoch (TT)	19770805.0	= JD 2443360.5
time of perihelion passage (TT)	19770721.555156	± 0.006685
perihelion distance	5.60632765	± 0.00003869
eccentricity	1.00294290	± 0.00006749
argument of perihelion [deg]	343.283932	± 0.000542
longitude of the ascending node [deg]	211.623628	± 0.000070
inclination [deg]	116.930129	± 0.000162
inverse semimajor axis [10^-6 au^-1]	-524.92	± 12.03

Notes: Epoch is given in a format: yyyymmdd.d, time of perihelion passage in a format of yyyymmdd.dddddd.

Figure caption: Six 2D-projections of the 6D space of original swarm (5001 VCs) of C/1978 A1. Each density map is given in logarithmic scale presented on the right in the individual panel.
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Original orbital elements (barycentric; at 250 au from the Sun)

Epoch (TT)	16701212
time of perihelion passage (TT)	19770722.686250	± 0.006476
perihelion distance	5.60844086	± 0.00003815
eccentricity	0.99978957	± 0.00006666
argument of perihelion [deg]	343.384843	± 0.000535
longitude of the ascending node [deg]	211.662760	± 0.000069
inclination [deg]	116.926807	± 0.000160
inverse semimajor axis [10^-6 au^-1]	37.52	± 11.89

Note: Values of uncertainties of original/future orbital elements were derived using a swarm of 5001 osculating orbits of VCs (including the nominal osculating orbit given above) for original/future orbital evolution calclulations and then by fitting the distribution of a given orbital element of original/future swarm of VCs to Gaussian distribution.

Original barycentric positions and velocities of 5001 VCs at 250 au from the Sun are given here (data format), i.e. before entering the planetary zone.

Future orbital elements (barycentric; at 250 au from the Sun)

Epoch (TT)	22820806
time of perihelion passage (TT)	19770722.474789	± 0.006619
perihelion distance	5.60423856	± 0.00003826
eccentricity	1.00054560	± 0.00006660
argument of perihelion [deg]	343.329066	± 0.000535
longitude of the ascending node [deg]	211.703824	± 0.000068
inclination [deg]	116.917447	± 0.000161
inverse semimajor axis [10^-6 au^-1]	-97.35	± 11.88