Wednesday, August 7, 2019

William Herschel Discovered NGC 6818, Little Gem Nebula, Aug. 8, 1787


Summary: Uranus discoverer William Herschel discovered lenticular galaxy NGC 665 Sept. 4, 1786, five years five-plus months after discovering Uranus March 13, 1781.


NGC 665 appears as II-588 in Uranus discoverer Sir William Herschel’s list of “II. Second Class. Faint Nebulae” discoveries; the lenticular galaxy in Pisces was the first of two galaxies that he discovered Sep. 4, 1786: Sloan Digital Sky Survey (SDSS), CC BY 4.0 International, via Wikimedia Commons

Uranus discoverer William Herschel discovered lenticular galaxy NGC 665 Sept. 4, 1786, five years five-plus months after his discovery of the solar system’s seventh planet, Uranus, which happened March 13, 1781.
German-British astronomer and composer Sir Frederick William Herschel (Nov. 15, 1738-Aug. 25, 1822) made his discovery of NGC 665 at his observatory residence, Observatory House, on Windsor Road in Slough, Royal County of Berkshire, south east England. Wolfgang Steinecke, Director of the Webb Deep-Sky Society’s Nebulae and Clusters Section, identifies the instrument used for the two consecutive discoveries as Herschel’s 20-foot, long-focus Newtonian reflector telescope. The model’s mirror measured 18.7 inches.
Sir William’s discovery Sept. 4, 1786, appear as number 588 under “II. Second Class. Faint Nebulae” in his Catalogue of a Second Thousand of New Nebulae and Clusters of Stars, published in 1789. He organized his discoveries of new nebulae and star clusters into eight classes. The first class comprised “Bright nebulae.” Classes three through eight itemized, respectively, “Very faint nebulae”; “Planetary nebulae”; “Very large nebulae”; “Very compressed and rich clusters of stars”; “Pretty much compressed clusters of large or small stars”; “Coarsely scattered clusters of stars.”
Sir William’s three deep-sky catalogues, published in 1786, 1789 and 1802, followed an identical format that included identifying “the star, or other object” that “is either preceding or following” the nebula. Object II-588 precedes “24 (ξ) Ariet,” a binary star in Aries the Ram constellation.
Sir William referenced the “determining star” by both Bayer and Flamsteed stellar designations. German celestial cartographer Johann Bayer (1572-March 7, 1625) specified stars with designators comprising a Greek or Latin letter preceding the genitive form of the parent constellation’s Latin name. The Bayer designation for the “determining star” is ξ Arietis (Xi Arietis), which is abbreviated as ξ Ari (Xi Ari). Devised by the United Kingdom’s first Astronomer Royal, John Flamsteed (Aug. 19, 1646-Dec. 31, 1719), the Flamsteed system designates stars with a number preceding the Latin genitive of the parent constellation. The Flamsteed designation for Xi Arietis is 24 Arietis.
According to Sir William’s observations, II-588 precedes Xi Arietis by a sidereal time of 39 minutes 40 seconds. His calculations determined the location of II-588 as 0 degrees 17 minutes south of the “determining star.”
Sir William indicated that he had made two observations of II-588. He used a system of abbreviations for describing his observations. Sir William perceived II-588 as “F. S. lE r. bM.” According to his code of abbreviations, his description of 588 translates as: “Faint. Small. A little extended, resolvable. Brighter in the middle.”
Sir William’s faint nebula number 588 is identified as NGC 665 in the New General Catalogue, published in 1888 by Danish-Irish astronomer John Louis Emil Dreyer (Feb. 13, 1852-Sept. 14, 1926). Dreyer’s compilation assigns NGC (New General Catalog) numbers to discoveries and observations by Sir William; his son, Sir John Frederick William Herschel, 1st Baronet (March 7, 1792-May 11, 1871); his sister, Caroline Herschel (March 16, 1750-Jan. 9, 1848); and other observational astronomers. The entries are presented in order of right ascension (celestial equivalent of terrestrial longitude).
NGC 665 is located in celestial equatorial constellation Pisces the Fishes. The galaxy’s equatorial coordinates are right ascension of 01 hour 44 minutes 56.10 seconds, declination of plus 10 degrees 25 minutes 22.9 seconds (epoch J2000.0), according to NASA/IPAC Extragalactic Database (NED).
The NED Database indicates that NGC 665 falls within the galaxy morphological classification designated as (R)S0^0, a lenticular galaxy with an outer ring. Ronald J. Buta, a University of Alabama astronomy professor specializing in galactic morphology, explains that outer rings are “occasionally seen enveloping the main bodies of early-type spirals and lenticulars.”
A lenticular galaxy (designated S0) displays an extended, disk-like structure surrounding a bright, central concentration, known as the bulge. NGC 665 is a 12th magnitude lenticular galaxy, according to the online Celestial Atlas of NGC Objects maintained by Courtney Seligman, Professor Emeritus of Astronomy at California’s Long Beach City College.
Object II-588 was the first of two galaxies discovered Sept. 4, 1786, by William Herschel. The second galaxy, object II-589, is now known as NGC 673 and lies in the neighboring constellation of Aries the Ram.
The takeaway for NGC 665, discovered Sept. 4, 1786, as II-588 by Uranus discoverer Sir William Herschel, is that lenticular galaxy claims Pisces the Fishes as parent constellation.

Hubble Space Telescope image of NGC 665; RA 01:44:56.49, DEC 10:25:28.3; Nov. 7, 2016; image ICV408JJQ: HLA (Hubble Legacy Archive) via HLA-STScI (Space Telescope Science Institute)

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

Image credits:
NGC 665 appeared as II.588 in Uranus discoverer Sir William Herschel’s list of “II. Second Class. Faint Nebulae” discoveries; the lenticular galaxy in Pisces was the first of two galaxies that he discovered Sep. 4, 1786: Sloan Digital Sky Survey (SDSS), CC BY 4.0 International, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:NGC665_-_SDSS_DR14.png
Hubble Space Telescope image of NGC 665; RA 01:44:56.49, DEC 10:25:28.3; Nov. 7, 2016; image ICV408JJQ: HLA (Hubble Legacy Archive) via HLA-STScI (Space Telescope Science Institute) @ https://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=ngc%20665

For further information:
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Available @ https://ia800501.us.archive.org/14/items/newgeneralcatalo00dreyrich/newgeneralcatalo00dreyrich.pdf
Available via HathiTrust @ https://hdl.handle.net/2027/osu.32435078053089?urlappend=%3Bseq=38
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Available @ https://ia800501.us.archive.org/14/items/newgeneralcatalo00dreyrich/newgeneralcatalo00dreyrich.pdf
Available via HathiTrust @ https://hdl.handle.net/2027/osu.32435078053089
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Available via JSTOR @https://www.jstor.org/stable/106695
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