# 84P/Giclas

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**84P/Giclas** is a [Jupiter-family comet](/source/List_of_numbered_comets) with a 6.69-year orbit around the [Sun](/source/Sun). It is the only comet discovered by American astronomer, [Henry L. Giclas](/source/Henry_L._Giclas).

## Observational history

### 1931 apparition

It was announced in 1995 that [Clyde W. Tombaugh](/source/Clyde_W._Tombaugh) had observed a previously unknown comet for three nights in September 1931.[2] Designated as **D/1931 R1**,[1] it was later confirmed to be an earlier apparition of 84P/Giclas upon reconstructing its orbit using non-gravitational accelerations in a 1996 study by [Grzegorz Sitarski](/source/Grzegorz_Sitarski).[5]

### 1979 apparition

The comet was discovered by [Henry L. Giclas](/source/Henry_L._Giclas) from the [Lowell Observatory](/source/Lowell_Observatory) on 8 September 1978.[6] At the time it was a diffuse 15th-magnitude object within the constellation [Cetus](/source/Cetus_(constellation)).[a] He confirmed his discovery about two days later,[7] where [Brian G. Marsden](/source/Brian_G._Marsden) soon determined that it follows a 6.74-year periodic orbit around the Sun.[8] Throughout its 1978–1979 apparition, it remained mostly a photographic object.[9]

### Follow-up observations

During the 2020 apparition, it was not more than 60 degrees from the Sun until September 2020. On 11 June 2033, the comet will pass 0.0387 astronomical units from the asteroid [4 Vesta](/source/4_Vesta).[10]

## Physical characteristics

Based on observations by the [Hubble Space Telescope](/source/Hubble_Space_Telescope) in 1999–2000, the [nucleus](/source/Comet_nucleus) of the comet has a radius of 0.90 ± 0.05 km, assuming a [geometric albedo](/source/Geometric_albedo) of 0.04.[3]

## Notes

1. Reported initial position upon discovery was: [α](/source/Right_ascension) = , [δ](/source/Declination) = [9]

## References

1. B. A. Skiff & D. H. Levy (1995-04-13). ["Comet D/1931 R1"](http://www.cbat.eps.harvard.edu/iauc/06100/06161.html). *IAU Circular*. **6161** (3). D. W. Green (ed.). [ISSN 0081-0304](https://www.worldcat.org/issn/0081-0304)

1. R. J. Bouma (1995-05-05). ["Comet 84P/Giclas"](http://www.cbat.eps.harvard.edu/iauc/06100/06168.html). *IAU Circular*. **6168** (4). D. W. Green (ed.). [ISSN 0081-0304](https://www.worldcat.org/issn/0081-0304)

1. P. L. Lamy; I. Toth; H. A. Weaver; M. F. A'Hearn; L. Jorda (2009). ["Properties of the nuclei and comae of 13 ecliptic comets from Hubble Space Telescope snapshot observations"](https://www.aanda.org/articles/aa/pdf/2009/47/aa11462-08.pdf). *Astronomy & Astrophysics*. **508** (2): 1045–1056. [Bibcode:2009A&A...508.1045L](https://ui.adsabs.harvard.edu/abs/2009A%26A...508.1045L). [doi:10.1051/0004-6361/200811462](https://doi.org/10.1051/0004-6361/200811462). [S2CID 125249770](https://api.semanticscholar.org/CorpusID:125249770)

1. ["Horizons Batch for 84P/Giclas (90000868) on 2027-Feb-12"](https://ssd.jpl.nasa.gov/api/horizons.api?format=text&COMMAND=%27DES%3D84P%3BCAP%27&START_TIME=%272027-Feb-10%27&STOP_TIME=%272027-Feb-14%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27) (Perihelion occurs when rdot flips from negative to positive). [JPL Horizons](/source/JPL_Horizons_On-Line_Ephemeris_System). Retrieved 2022-06-19. (JPL#49 Soln.date: 2021-Mar-29)

1. G. Sitarski (1996). ["On the Identity of the Periodic Comets 84P/Giclas and D/1931 R1"](https://acta.astrouw.edu.pl/Vol46/n1/pap_46_1_6.pdf). *Acta Astronomica*. **46** (1): 47–49. [Bibcode:1996AcA....46...47S](https://ui.adsabs.harvard.edu/abs/1996AcA....46...47S)

1. H. L. Giclas & M. L. Kantz (1978-09-13). ["Comet Giclas (1978k)"](http://www.cbat.eps.harvard.edu/iauc/03200/03264.html). *IAU Circular*. **3264** (2). B. G. Marsden (ed.). [Bibcode:1978IAUC.3264....2G](https://ui.adsabs.harvard.edu/abs/1978IAUC.3264....2G)

1. H. L. Giclas & M. L. Kantz (1978-09-14). ["Comet Giclas (1978k)"](http://www.cbat.eps.harvard.edu/iauc/03200/03266.html). *IAU Circular*. **3266** (1). B. G. Marsden (ed.). [Bibcode:1978IAUC.3266....1G](https://ui.adsabs.harvard.edu/abs/1978IAUC.3266....1G)

1. C. Y. Shao (1978-09-18). ["Periodic Comet Giclas (1978k)"](http://www.cbat.eps.harvard.edu/iauc/03200/03269.html). *IAU Circular*. **3269** (2). B. G. Marsden (ed.). [Bibcode:1978IAUC.3269....2S](https://ui.adsabs.harvard.edu/abs/1978IAUC.3269....2S)

1. G. W. Kronk & M. Meyer (2010). [*Cometography: A Catalog of Comets*](https://books.google.com/books?id=qV4Q49x8PTsC&pg=PA613). Vol. 5: 1960–1982. Cambridge University Press. pp. 613–614. ISBN 978-0-521-87226-3.

1. ["84P/Giclas – JPL Small-Body Database Lookup"](https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=84P). *ssd.jpl.nasa.gov*. [Jet Propulsion Laboratory](/source/Jet_Propulsion_Laboratory). Retrieved 2012-02-18.

## External links

- [84P/Giclas](https://cometography.com/pcomets/084p.html) at Gary W. Kronk's *Cometography*
- [84P/Giclas](http://www.aerith.net/comet/catalog/0084P/index.html) at Seiichi Yoshida's website
- [84P/Giclas](http://www.oaa.gr.jp/~oaacs/nk/nk1911.htm) at Syuichi Nakano's website

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Adapted from the Wikipedia article [84P/Giclas](https://en.wikipedia.org/wiki/84P%2FGiclas) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/84P%2FGiclas?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.