Sir John Herschel Made Three Observations of the Bow Tie Nebula NGC 40

Summary: John Herschel made three observations of the Bow Tie Nebula NGC 40, the planetary nebula discovered Nov. 25, 1788, by his father, William Herschel.

On Dec. 20, 1829, English polymath Sir John Herschel made his first of three observations of NGC 40, a planetary nebula in constellation Cepheus discovered by his father, Uranus discoverer Sir William Herschel, Nov. 25, 1788; 1829 miniature watercolor of John Herschel by Swiss portrait painter Alfred Edward Chalon, painted as complement to portrait of Margaret Brodie Stewart (Aug. 16, 1810-Aug. 3, 1884) for their marriage March 3, 1829: Public Domain, via Wikimedia Commons

Sir John Herschel made three observations of the Bow Tie Nebula NGC 40, a planetary nebula in Cepheus the King constellation discovered Nov. 25, 1788, by his father, Sir William Herschel.

German-British astronomer and composer Sir Frederick William Herschel (Nov. 15, 1738-Aug. 25, 1822) discovered NGC 40 seven years eight-plus months after his March 13, 1781, discovery of Uranus, the solar system’s seventh planet. Sir William made his discovery of NGC 40 at his last residence, known as Observatory House, in Slough, Royal County of Berkshire, South East England.

Sir William’s discovery of NGC 40 appears in his Catalogue of a Second Thousand of New Nebulae and Clusters of Stars, published in 1789. The discovery is entered as number 58 in the category of "IV. Fourth claſs. Planetary nebulae.”

Sir William’s only child, English polymath Sir John Frederick William Herschel, 1st Baronet (March 7, 1792-May 11, 1871), shared his father’s interest in astronomy. In 1852, Sir John named the four then-known moons of his father’s planet: Ariel, Umbriel, Titania and Oberon.

In 1833, Sir John published Observations of Nebulae and Clusters of Stars, Made at Slough, With a Twenty-Feet Reflector, Between the Years 1825 and 1833. The astronomical catalogue comprised his and his father’s observations. He arranged the catalogue’s entries “in order of right ascension,” the celestial equivalent of terrestrial longitude.

Sir William’s Cepheid planetary nebula appears as entry number 8 in Sir John’s 1833 publication. Sir William’s designation for his discovery, IV-58, is given as the synonym for entry number 8. Sir John noted three observations of his entry number 8.

The observations were made during sweeps 228, 378 and 380. Sweep 228 occurred Dec. 20, 1829. Sweep 378 took place Oct. 29, 1831. On Nov. 2, 1831, Sir John conducted sweep 380. Sir William and Sir John referred to their telescopic surveys of the sky as “sweeps of the heavens.”

Sir John began entry number 8 with details from sweep 378 (Oct. 29, 1831), which occurred chronologically as the second of his three observations. He described his observation of IV-58 as: “A * 10 m with strong neb atmosph 15” diameter. Exactly R and p suddenly fading away makes a D * class 5 with a * preceding.” His description translates as: “A star of the 10th magnitude with strong nebulous atmosphere, diameter of 15 arc seconds. Exactly round and pretty, suddenly fading away, makes a class 5 double star with a preceding star.”

The second set of details for entry number 8 came from sweep 380 (Nov. 2, 1831), which was actually the third, or most recent, of his three observations. His second observation remarked: “The L * of a D * strongly affected with a neb burr. Pos 241°^.4; △ AR = 25^s; 10 and 12 m.” His description translates as: “The large star of a double star strongly affected with a nebulous burr. Angle of position measured 241°^.4 by the micrometer; right ascension 25 seconds. 10th and 12th magnitude.”

Sweep 228 (Dec. 20, 1829), which chronologically marked Sir John’s first sighting of IV-58, supplied the third set of details for entry number 8. Sir John noted: “A star 11 m with a luminous atm 30 or 40” diam.” His description translates as: “A star of the 11th magnitude with a luminous atmosphere, diameter of 30 or 40 arcseconds.”

In 1865, Sir John published Catalogue of Nebulae and Clusters of Stars. The catalogue’s entry number 20 links with his 1833 catalogue’s entry number 8 and with Sir William’s IV-58 entry. He constructed his descriptions in the 1865 catalogue by assembling and comparing all observations and remarks given in his and his father’s catalogues. Sir John’s composite description of object IV-58 derived from his father’s sole discovery observation and from Sir John’s three observations.

Entry number 20 bears the composite description: “vF; vS; R; vsmbM *10; *12 241°^.4; 25^s.” The description translates as: “Very faint; very small; round; very suddenly much brighter in the middle, star of the 10th magnitude; star of the 12th magnitude, micrometrically measured 241°.4; 25 seconds.”

Sir William’s IV-58 and Sir John’s synonymous entries are now known as NGC 40. Danish-Irish astronomer John Louis Emil Dreyer (Feb. 13, 1852-Sept. 14, 1926) published A New General Catalogue in 1888 as a compilation of discoveries and observations by the father-and-son Herschels; Sir William’s sister Caroline (March 16, 1750-Jan. 9, 1848); and other observational astronomers.

The takeaway for Sir John Herschel’s three observations of the Bow Tie Nebula NGC 40 is that the English polymath’s observations revisited the Cepheid planetary nebula discovered Nov. 25, 1785, by his father, Uranus discoverer Sir William Herschel.

Hubble Space Telescope WFPC2 (Wide Field Planetary Camera 2) color image of NGC 40 (lower left), with the planetary nebula's central star; RA 00:12:56.42, DEC 72:31:37.0; Nov. 10, 1995; image NGC40 (color) WFPC2 f814w/f555w PC1 06119_01: 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:

On Dec. 20, 1829, English polymath Sir John Herschel made his first of three observations of NGC 40, a planetary nebula in constellation Cepheus discovered by his father, Uranus discoverer Sir William Herschel, Nov. 25, 1788; 1829 miniature watercolor of John Herschel by Swiss portrait painter Alfred Edward Chalon, painted as complement to portrait of Margaret Brodie Stewart (Aug. 16, 1810-Aug. 3, 1884) for their marriage March 3, 1829: Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:John_Herschel00.jpg

Hubble Space Telescope WFPC2 (Wide Field Planetary Camera 2) color image of NGC 40 (lower left), with the planetary nebula's central star; RA 00:12:56.42, DEC 72:31:37.0; Nov. 10, 1995;  image NGC40 (color) WFPC2 f814w/f555w PC1 06119_01: 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%2040

For further information:

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Available via HathiTrust @ https://hdl.handle.net/2027/osu.32435078053089

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