Sir John Herschel Observed NGC 7479 in October 1823 and October 1830

Summary: Sir John Herschel observed NGC 7479 in October 1823 and October 1830, over four decades after his father’s Oct. 19, 1784, discovery of the galaxy.

NGC 7479, imaged with SBIG STL11000 CCD Camera, 24-inch RC Optical Systems Telescope, Mount Lemmon SkyCenter, Santa Catalina Mountains, Coronado National Forest, southeastern Arizona; September 2010: Adam Block/Mount Lemmon SkyCenter/University of Arizona, CC BY SA 3.0 United States, via Wikimedia Common

Sir John Herschel observed NGC 7479 in October 1823 and October 1830, over four decades after his father’s Oct. 19, 1784, discovery of the barred spiral galaxy in constellation Pegasus.

German-British astronomer and composer Sir Frederick William Herschel (Nov. 15, 1738-Aug. 25, 1822) discovered NGC 7479 three years seven-plus months after his March 13, 1781, discovery of solar system planet number seven, Uranus. Sir William recorded his discovery of NGC 7479 in his Catalogue of One Thousand New Nebulae and Clusters of Stars, published in 1786. The discovery appears as number 55 in the category of “Firſt claſs. Bright nebulae.”

John Frederick William Herschel, 1st Baronet (March 7, 1792-May 11, 1871), shared his father’s interest in astronomy. Sir William’s only child also kept written records of his own discoveries and observations.

Observations of his father’s Pegasid barred spiral galactic discovery appear in two of Sir John’s astronomical catalogues in which he collated his discoveries and observations with those of his father. In 1833, he published Observations of Nebulae and Clusters of Stars, Made at Slough, With a Twenty-Feet Reflector, Between the Years 1825 and 1833. In 1864, Sir John published Catalogue of Nebulae and Clusters of Stars. Both catalogues appeared in the Philosophical Transactions of the Royal Society of London.

Entry number 2205 in Observations of Nebulae and Clusters of Stars (1833) is synonymized with “I.55,” known now as NGC 7479. Sir John details four observations that he made during four astronomical “sweeps,” or surveys. Sweeps 13 and 14 took place Oct. 12 and Oct. 13, respectively, in 1823. Sweeps 304 and 305 were conducted Oct. 9 and Oct. 10, respectively, in 1830.

Sir John arranged his entries in order of right ascension (the celestial equivalent of terrestrial longitude). Accordingly, the observation from Sweep 14 (Oct. 13, 1825) appears first. The right ascension is calculated at 22 hours 56 minutes 24.0 seconds, and the declination is 78 degrees 35 minutes 19 seconds (epoch J1830.0). He described “I.55” as: “p B; irreg R; r; I see 2 or 3 stars in it; E between 2 stars. (See fig 63.).” His description translates as: “Pretty Bright; irregularly round; resolvable; I see two or three stars in it; extended between two stars.”

Sir John’s observations during Sweep 304 (Oct. 9, 1830) appear next. Right ascension is 22 hours 56 minutes 26.0 seconds, and the declination is 78 degrees 35 minutes 30 seconds. Sir John remarked: “B; m E; pos by micr = 192°.0; p g m b M; has a * 12 m n p; a large * s, and one or two 15.16 m in or near the middle.” His description translates as: “Bright; much extended; angle of position measured 192°.0 by the micrometer; pretty gradually much brighter in the middle; has a star of the 12th magnitude north preceding; a large star south, and one or two 15.16 magnitude in or near the middle.”

The observation of NGC 7479 during Sweep 305 (Oct. 10, 1830) gives right ascension of 22 hours 56 minutes 26.9 seconds and declination of 78 degrees 35 minutes 35 seconds. The description notes: “p B; m E, pos by micr = 11°.8 (= 191.8); 2’ l, 30” br; between 2 small stars. Has two v S stars in it.” The description transcribes as: “Pretty bright; much extended; angle of position measured 11°.8 (= 191.8) by micrometer; 2 minutes long, 30 seconds broad; between two small stars. Has two very small stars in it.”

The last observation under Sir John’s entry number 2205 comes from Sweep 13, chronologically the first observation with a date of Oct. 12, 1823. Right ascension measures 22 hours 56 minutes 28.8 seconds, and declination is figured at 78 degrees 35 minutes 50 seconds. The description states: “p F; b M; E in merid between 2 stars; 90” l, 40” br.” The expanded description reads: “Pretty faint; bright in the middle; extended in the meridian between two stars; 90 seconds long, 40 seconds broad.”

Sir John detailed NGC 7479 as entry number 4892 in his Catalogue of Nebulae and Clusters of Stars (1864). He synonymized 4892 with his previous catalogue’s entry number 2205 and with his father’s entry as “I.55.” His compressed description observes: “pB; cL; mE 11°9; bet 2 st.” The observation expands as: “Pretty bright; considerably large; much extended, 11°9; between two stars.”

The designation of Sir William’s barred spiral galaxy in Pegasus the Winged Horse constellation as NGC 7479 reflects the entry number for I-55 in the New General Catalogue by Danish-Irish astronomer John Louis Emil Dreyer (Feb. 13, 1852-Sept. 14, 1926). Published in 1888, Dreyer’s catalogue is a compilation of the discoveries and observations of the Herschels (Sir William; his astronomer sister Caroline; his son John) and other observational astronomers.

The takeaway for Sir John Herschel’s observations of NGC 7479 in October 1823 and in October 1830 is that, over four decades after Uranus discoverer William Herschel’s Oct. 19, 1784, discovery of the barred spiral galaxy in Pegasus, his son added four detailed observations to NGC 7479’s observational history.

Hubble Space Telescope Wide Field Planetary Camera image of NGC 7479; RA 23:04:56.08, DEC 12:19:20.9; Oct. 16, 1995; image NGC 7479 hst_06266_01_wfpc2_total_pc: HLA (Hubble Legacy Archive) ia 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:

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

Image credits:

NGC 7479, imaged with SBIG STL11000 CCD Camera, 24-inch RC Optical Systems Telescope, Mount Lemmon SkyCenter, Santa Catalina Mountains, Coronado National Forest, southeastern Arizona; September 2010: Adam Block/Mount Lemmon SkyCenter/University of Arizona, CC BY SA 3.0 United States, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:N7479s.jpg

Hubble Space Telescope Wide Field Planetary Camera image of NGC 7479; RA 23:04:56.08, DEC 12:19:20.9; Oct. 16, 1995; image NGC 7479 hst_06266_01_wfpc2_total_pc: HLA (Hubble Legacy Archive) ia HLA-STScI (Space Telescope Science Institute) @ http://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=ngc%207479

For further information:

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