Uranian Irregular Moons Caliban and Sycorax Were Discovered Sept. 6, 1997

Summary: Uranian irregular moons Caliban and Sycorax were discovered Sept. 6, 1997, via Palomar Observatory’s 200-inch (5.1-meter) Hale Telescope.

artist’s concept of Sycorax, created with Celestia software Sunday, May 8, 2011: Lanthanum-138, Public Domain, via Wikimedia Commons

Uranian irregular moons Caliban and Sycorax were discovered Sept. 6, 1997, via the 200-inch (5.1-meter) Hale Telescope, which is housed southeast of Los Angeles at the California Institute of Technology’s (Caltech) Palomar Observatory.

The discoveries of “two probable distant satellites of Uranus” were announced by Brian G. (Geoffrey) Marsden, director of the Central Bureau for Astronomical Telegrams (CBAT) in IAUC (International Astronomical Union Circular) no. 6764, dated Oct. 31, 1997. Marsden assigned provisional designations of S/1997 U 1 and S/1997 U 2 to the Uranian satellite discoveries.

Marsden identified the discoverers as B.J. (Brett James) Gladman of the Canadian Institute for Theoretical Astrophysics (CITA) in Toronto, Ontario, Central Canada; P.D. (Philip David) Nicholson and J.A. (Joseph Arthur) Burns of Cornell University in Ithaca, Finger Lakes region, Central New York; and J.J. (John “JJ”) Kavelaars of McMaster University in Hamilton, Ontario, Central Canada. In early October Gladman had detected the satellites on a set of 12 CCD (charged-couple detector) frames obtained Sept. 6 and 7 with the COSMIC camera on the 5.1-meter (200-inch) Hale Telescope.

The fainter satellite, S/1997 U 1, was positioned about 6 arcminutes east of Uranus. The brighter satellite, S/1997 U 2, was located about 7 arcminutes west-northwest of Uranus.

Gladman’s team posted coordinates, epoch 2000, for S/1997 U 1, for Sept. 6 and 7. For Sept. 6.21723, the faint satellite registered right ascension (abbreviated RA; symbol α) of 20 hours 31 minutes 52.90 arcseconds and declination (abbreviated dec; symbol δ) of minus 19 degrees 33 arcminutes 24.4 arcseconds. Its right ascension and declination for Sept. 7.20042 measured 20 hours 31 minutes 45.88 seconds and minus 19 degrees 33 arcminutes 52.2 arcseconds, respectively.

Nicholson’s team posted coordinates, epoch 2000, for S/1997 U2, for Sept. 6 and 7. For Sept. 6.22938, the bright satellite was at right ascension 20 hours 30 minutes 59.93 seconds and declination minus 19 degrees 30 arcminutes 51.9 arcseconds. For Sept. 7.20902, S/1997 U 2 was found at right ascension 20 hours 30 minutes 53.31 seconds and declination minus 19 degrees 31 arcminutes 13.3 arcseconds.

Marsden noted that the discoverers reobserved their finds with the Hale Telescope in late October. Two reobservations were achieved for S/1997 U 2, but “bad seeing” allowed for only one night’s detection of S/1997 U 1.

Gladman’s team reobserved S/1997 U 1 Oct. 27.14067 at right ascension 20 hours 29 minutes 34.32 seconds, declination minus 19 degrees 42 minutes 44.7 seconds. Marsden commented that the satellite’s position differed by "some 30"" from Nicholson’s prediction, which had been based upon “a circular uranicentric orbit.”

Nicholson’s team reobserved S/1997 U 2 on Oct. 28 and 29. For Oct. 27.16834, S/1997 U 2 appeared at right ascension 20 hours 29 minutes 06.15 seconds, declination minus 19 degrees 35 arcminutes 56.5 arcseconds. For Oct. 28.14304, it was detected at right ascension 20 hours 29 minutes 09.11 seconds, declination minus 19 degrees 35 arcminutes 44.6 arcseconds.

In IAUC no. 7132, dated March 27, 1999, Marsden referenced the first two Uranian irregular satellite discoveries by their official and proposed names. Uranus XVI, the IAU’s official sequential designation for the fainter satellite, S/1997 U 1, reflects the fainter satellite’s status as the 16th satellite discovery in the Uranian system. Uranus XVII indicates that S/1997 U 2 numbers as the Uranian system’s 17th satellite discovery.

The discoverers suggested Caliban as the name for Uranus XVI (S/1997 U 1) and Sycorax as the name for Uranus XVII (S/1997 U 2). Caliban is the misshapen son of the exiled Algerian witch Sycorax in “The Tempest” by Elizabethan playwright William Shakespeare (bapt. April 26, 1564-April 23, 1616).

The IAU’s Gazetteer of Planetary Nomenclature website, maintained by the U.S. Geological Survey’s Astrogeology Science Center, states that characters in “The Rape of the Lock” by 18th-century English poet Alexander Pope (May 21, 1688-May 30, 1744) and in Shakespearean plays inspire the names of the Uranian system’s satellites. Official approval of Caliban and Sycorax occurred during the IAU’s XXIVth (24th) General Assembly, held Monday, Aug. 7, to Friday, Aug. 18, 2000, in Manchester, United Kingdom.

The takeaways from the Sept. 6, 1997, discoveries of Uranian irregular moons Caliban and Sycorax are that the first two irregular satellites in the Uranian system were discovered on frames obtained by the Hale Telescope’s COSMIC camera at California’s Palomar Observatory; that their official designations of Uranus XVI and Uranus XVII denote their rank as the 16th and 17th satellite discoveries in the Uranian system; and that the satellites’ names observe the convention of namesaking characters in 18th-century English poet Alexander Pope’s “The Rape of the Lock” and in Elizabeth playwright William Shakespeare’s plays.

artist’s concept of Caliban, created with Celestia software; Aug. 6, 2011: Lanthanum-138, CC 1.0 Universal (CC0 1.0) Public Domain dedication, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

artist’s concept of Sycorax, created with Celestia software Sunday, May 8, 2011: Lanthanum-138, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Sycorax.png

artist’s concept of Caliban, created with Celestia software; Aug. 6, 2011: Lanthanum-138, CC 1.0 Universal (CC0 1.0) Public Domain dedication, via Wikimedia Commons @ https://en.wikipedia.org/wiki/File:Caliban_artistic.png

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