C/1975 V1 (West)

Observational history

It was discovered photographically by Richard M. West, of the European Southern Observatory, on 10 August 1975. The comet came to perihelion (closest approach to the Sun) on 25 February 1976. During perihelion the comet had a minimum solar elongation of 6.4° and as a result of forward scattering reached a peak apparent magnitude of −3. From 25 to 27 February, observers reported that the comet was bright enough to study during full daylight.

Despite its brightness, Comet West went largely unreported in the popular media. This was partly due to the relatively disappointing display of Comet Kohoutek in 1973, which had been widely predicted to become extremely prominent: scientists were wary of making predictions that might raise public expectations.

The New York Times, however, reported this about Comet West on 2 March 1976:

Breakup

Before the perihelion passage, and using 28 positions obtained between 10 August 1975 and 27 January 1976, Comet West was estimated to have an orbital period of about 254,000 years. As the comet passed within 30 million km of the Sun, the nucleus was observed to split into four fragments.

The first report of the split came around 7 March 1976 at 12:30 UTC, when reports were received that the comet had broken into two pieces. Astronomer Steven O'Meara, using the 9-inch Harvard Refractor, reported that two additional fragments had formed on the morning of 18 March.

The fragmentation of the nucleus was, at the time, one of very few comet breakups observed, one of the most notable previous examples being the Great Comet of 1882, a member of the Kreutz Sungrazing 'family' of comets. More recently, comets Schwassmann-Wachmann-3 (73P), C/1999 S4 LINEAR, and 57P/du Toit-Neujmin-Delporte, have been observed to split or disintegrate during their passage close to the Sun.

Orbit

With a nearly parabolic trajectory, estimates for the orbital period of this comet have varied from 254,000 to 558,000 years. Computing the best-fit orbit for this long-period comet is made more difficult since it underwent a splitting event which may have caused a non-gravitational perturbation of the orbit. The 2008 SAO Catalog of Cometary Orbits shows 195 observations for C/1975 V1 and 135 for C/1975 V1-A, for a combined total of 330 (218 observations were used in the fit).

The comet has been more than 50 AU from the Sun since 2003.

Physical characteristics

A 2014 reanalysis of photometric observations of the comet during its perihelion in 1976 revealed that the dust particles emitted from its coma were a mixture of weakly refractive and highly refractive material, indicating the presence of Mg-rich silicates and amorphous carbon within the comet itself. The observed morphology of agglomerated debris is consistent to those found in other comets like 1P/Halley and Hale–Bopp.

Emission lines of , CN, , CH, and were detected from the comet. Photometric observations of the comet's fragments about two months after it split apart had revealed an uneven distribution of the aforementioned compounds, indicating that the original nucleus was heterogeneous with significant composition variations in some areas.

Nomenclature

In the nomenclature of the time, it was known as Comet 1976 VI or Comet 1975n, but the modern nomenclature is C/1975 V1. (Note that "1976 VI" uses the Roman numeral VI = 6, while "C/1975 V1" is the letter V and the number 1).

Notes

References

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