Wednesday, October 16, 2019

William Herschel Discovered Barred Spiral Galaxy NGC 7479 Oct. 19, 1784


Summary: William Herschel discovered barred spiral galaxy NGC 7479 Oct. 19, 1784, three years seven-plus months after his March 13, 1781, discovery of Uranus.


Uranus discoverer Sir William Herschel discovered barred spiral galaxy NGC 7479 in constellation Pegasus Oct. 19, 1784; image of NGC 7479 “created from observations at visible and near-infrared wavelengths”; three brightest stars are “foreground stars -- caught on camera because they lie between the galaxy and Hubble”; NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys’ Wide Field Channel; image ID potw1125a; image release date 20 June 2011, 10:00; image credit ESA/Hubble & NASA: CC BY 4.0 International, via NASA ESA Hubble

Sir William Herschel discovered barred spiral galaxy NGC 7479 Oct. 19, 1784, three years seven-plus months after his March 13, 1781, discovery of the solar system’s seventh planet, Uranus.
Sir William (Nov. 15, 1738-Aug. 25, 1822) made his discovery of the barred spiral galaxy now known as NGC 7479 at his residence in Datchet, Royal County of Berkshire, South East England. He and his astronomer sister Caroline (March 16, 1750-Jan. 9, 1848) lived in the village from Aug. 1, 1782, until their move to Clay Hall, in Old Windsor, in June 1785.
The telescope that Sir William used was his 20-foot reflector. The long-focus Newtonian-styled model had an 18.7 inch-aperture.
Sir William’s Oct. 19, 1784, galactic discovery appears in his Catalogue of One Thousand New Nebulae and Clusters of Stars, published in 1786. He entered his discovery as number 55 under the category of “Firſt claſs. Bright nebulae.”
Sir William identified “66 Pegaſi” as “the ſtar, or other object, by which the place has been determined.” He determined that I-55 precedes 66 Pegasi by a sidereal time of 17 minutes 59 seconds. The galaxy lies 0 degrees 2 minutes to the north of 66 Pegasi.
Sir William made three observations of I-55. He described his discovery as: “cB. mE. Mer. gbM. 4’l. 2’b.” His abbreviated description translates as: “Considerably bright. Much extended in the direction of the meridian of the nebula. Gradually brighter in the middle. 4 minutes long. 2 minutes broad.”
Object I-55 appears as NGC 7479 in the New General Catalogue, published in 1888 by Danish-Irish astronomer John Louis Emil Dreyer (Feb. 13, 1852-Sept. 14, 1926). Dreyer’s catalogue organizes the discoveries and observations of the Herschels (Sir William; his astronomer sister Caroline; his son John) and other observational astronomers into a system ordered by right ascension (celestial equivalent of terrestrial longitude), with assigned NGC (New General Catalogue) numbers.
NGC 7479 is located in Pegasus the Winged Horse, a constellation in the Northern Celestial Hemisphere. The Winged Horse’s southern borders lie about two degrees from the celestial equator. The galaxy’s equatorial coordinates are right ascension 23 hours 04 minutes 49.61 seconds, declination plus 12 degrees 20 minutes 37.3 seconds (epoch J2000.0), according to NASA/IPAC Extragalactic Database (NED).
NGC 7479 classifies as having a galaxy morphology of SB(s)c, according to SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data), an astronomical database of extrasolar objects maintained by France’s Centre de Données Astronomiques de Strasbourg (CDS; Strasbourg Astronomical Data Center). The classification denotes a barred spiral galaxy (SB), without rings (s) and with very loosely wound arms (c). NGC 7479 is an 11th magnitude galaxy, according to Seppo Laine, research scientist at Spitzer Science Center, and Courtney Seligman, Professor Emeritus of Astronomy at California’s Long Beach City College.
The Hipparcos designation for 66 Pegasi (66 Peg), Sir William’s “determining star” for I-55, is HIP 115444. Released in June 1997, the Hipparcos Catalogue provides precise astrometric data for 118,218 stars. The catalogue’s data originates from Hipparcos (High Precision Parallax Collecting Satellite), a scientific satellite launched Aug. 8, 1989, by the European Space Agency (ESA) and deactivated Aug. 15, 1993.
The equatorial coordinates for HIP 115444 are right ascension 23 hours 23 minutes 04.567 seconds and declination plus 12 degrees 18 minutes 50.07 seconds (epoch J2000), according to Hubble Legacy Archive (HLA). Hubble Legacy Archive is an online project of Hubble products jointly administered by the Space Telescope Science Institute (STScI), the Space Telescope European Coordinating Facility (ST-ECF) and the Canadian Astronomy Data Centre (CADC).
Fifth magnitude binary star 66 Pegasi and barred spiral galaxy NGC 7479 lie south of Pegasus the Winged Horse constellation’s Great Square of Pegasus asterism, or recognizable pattern of stars. NGC 7479 lies 2.9 degrees south of Alpha Pegasi, according to Astronomy magazine senior editor Michael E. Bakich.
Alpha Pegasi (α Pegasi; Alpha Peg; α Peg) belongs to the starry quartet forming the Winged Horse’s Great Square asterism. Alpha Pegasi shines as the third brightest star in constellation Pegasus. Its IAU (International Astronomical Union) approved traditional name is Markab, either derived from Arabic for “saddle of the horse" or mistranscribed from Arabic for "shoulder of the horse."
The takeaway for Uranus discoverer Sir William Herschel’s discovery of barred spiral galaxy NGC 7479 Oct. 19, 1784, is that Sir William’s celestial object I-55 lies strategically south of Pegasus the Winged Horse constellation’s distinctive Great Square of Pegasus asterism.

Hubble Space Telescope Wide Field Camera image of NGC 7479; RA 23:04:54.69, DEC 12:19:43.6; Monday, Oct. 25, 2010; image NGC7479 hst_11575_53 ACS/WFD (color) SN2009JF f814w/f555w: 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:
Uranus discoverer Sir William Herschel discovered barred spiral galaxy NGC 7479 in constellation Pegasus Oct. 19, 1784; image of NGC 7479 “created from observations at visible and near-infrared wavelengths”; three brightest stars are “foreground stars -- caught on camera because they lie between the galaxy and Hubble”; NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys’ Wide Field Channel; image ID potw1125a; image release date 20 June 2011, 10:00; image credit ESA/Hubble & NASA: CC BY 4.0 International, via NASA ESA Hubble @ https://www.spacetelescope.org/images/potw1125a/
Hubble Space Telescope Wide Field Camera image of NGC 7479; RA 23:04:54.69, DEC 12:19:43.6; Monday, Oct. 25, 2010; image NGC7479 hst_11575_53 ACS/WFD (color) SN2009JF f814w/f555w: HLA (Hubble Legacy Archive), via HLA-STScI (Space Telescope Science Institute) @ http://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=ngc%207479

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