 Comet West photographed from theEuropean Southern Observatory on 9 March 1976 | |
| Discovery | |
|---|---|
| Discovered by | Richard M. West |
| Discovery site | European Southern Observatory |
| Discovery date | 10 August 1975 |
| Designations | |
| 1976 VI, 1975n | |
| Orbital characteristics[1] | |
| Epoch | 10 May 1976 (JD 2442908.5) |
| Observation arc | 199 days |
| Number of observations | 113 |
| Aphelion | 1,500 AU (inbound) |
| Perihelion | 0.197 AU |
| Eccentricity | 0.99997 |
| Orbital period | ~558,000 years |
| Inclination | 43.074° |
| 118.92° | |
| Argument of periapsis | 358.43° |
| Last perihelion | 25 February 1976 |
| TJupiter | 0.402 |
| EarthMOID | 0.555 AU |
| JupiterMOID | 1.194 AU |
| Physical characteristics[2] | |
Mean radius | 1.485 km (0.923 mi)[a] |
| Comet total magnitude (M1) | 5.6 |
| –3.0 (1976 apparition)[3] | |
Comet West, formally designated asC/1975 V1,1976 VI, and1975n, was acomet described as one of the brightest objects to pass through the innerSolar System in 1976. It is often described as a "great comet."[4]
It was discovered photographically byRichard M. West, of theEuropean Southern Observatory, on 10 August 1975. The comet came toperihelion (closest approach to the Sun) on 25 February 1976.[1] During perihelion the comet had a minimum solar elongation of 6.4° and as a result offorward scattering reached a peakapparent magnitude of −3.[3] From 25 to 27 February, observers reported that the comet was bright enough to study during full daylight.[3]
Despite its brightness, Comet West went largely unreported in the popular media. This was partly due to the relatively disappointing display ofComet Kohoutek in 1973, which had been widely predicted to become extremely prominent: scientists were wary of making predictions that might raise public expectations.[5]
The New York Times, however, reported this about Comet West on 2 March 1976:[6]
From tomorrow until Sunday a comet that may prove one of the brightest in this decade is expected to reach maximum visibility in the eastern sky before sunrise. ... By Wednesday,Dr. Marsden believes, it will be far enough from the sun to be visible to the unaided eye
— Walter Sullivan,The New York Times (2 March 1976)
Before theperihelion 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.[3] As the comet passed within 30 million km of the Sun, the nucleus was observed to split into four fragments.[7]
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.[citation needed]
The fragmentation of the nucleus was, at the time, one of very few comet breakups observed, one of the most notable previous examples being theGreat Comet of 1882, a member of theKreutz Sungrazing 'family' of comets. More recently, cometsSchwassmann-Wachmann-3 (73P),C/1999 S4 LINEAR, and57P/du Toit-Neujmin-Delporte, have been observed to split or disintegrate during their passage close to the Sun.[citation needed]
With a nearlyparabolic trajectory, estimates for theorbital period of this comet have varied from 254,000[3] to 558,000 years.[8] Computing thebest-fit orbit for this long-period comet is made more difficult since it underwent asplitting event which may have caused a non-gravitationalperturbation of the orbit. The 2008SAO 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 (7.5 billion km) from the Sun since 2003.[9]
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 ofMg-rich silicates and amorphouscarbon within the comet itself.[10] The observed morphology of agglomerated debris is consistent to those found in other comets like1P/Halley andHale–Bopp.[10]
Emission lines ofC2,CN,C3,CH, andNH2 were detected from the comet.[11] 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 originalnucleus was heterogeneous with significant composition variations in some areas.[11]
In the nomenclature of the time, it was known asComet 1976 VI orComet 1975n, but the modern nomenclature isC/1975 V1. (Note that "1976 VI" uses the Roman numeral VI = 6, while "C/1975 V1" is the letter V and the number 1).
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