Globular Cluster NGC 5634 Lies Midway Between Iota and Mu Virginis

Summary: Globular cluster NGC 5634 lies midway between Iota Virginis and Mu Virginis in southeastern Virgo the Virgin constellation.

Sir William Herschel’s 1785 discovery of Virgo’s only globular cluster, NGC 5634, occurred almost four years after his 1781 discovery of Uranus; 2.2 arcmin wide image of NGC 5634’s northwestern part: Hubble Legacy Archive, Public Domain, via Wikimedia Commons

Globular cluster NGC 5634 lies midway between Iota Virginis and Mu Virginis, stars with naked eye visibility in southeastern Virgo the Virgin constellation, near Virgo’s border with northwestern Libra the Scales constellation.

Fourth magnitude stars Iota Virginis and Mu Virginis star hop binocular and telescopic observers to globular cluster NGC 5634. Lying east of yellowish Iota Virginis, bluish-white Mu Virginis hovers near the southeastern Virgo-northwestern Libra border.

Celestial coordinates for Iota Virginis are right ascension (RA; similar to geographic longitude) at 14 hours 16 minutes 00.866 seconds and declination (DEC; similar to geographic latitude) at minus 6 degrees 00 minutes 02.01 seconds, according to Hubble Legacy Archive (HLA). HLA celestial coordinates for Mu Virginis are right ascension at 14 hours 43 minutes 03.618 seconds and declination at minus 5 degrees 39 minutes 29.59 seconds. NGC 5634’s right ascension is 14 degrees 29 minutes 37.279 seconds, with declination at minus 5 degrees 58 minutes 35.15 seconds, according to Hubble Legacy Archive.

Both stars participate in the recently discovered February mu Virginid (FMV) meteor shower as radiants. Mu Virginis is the shower’s namesake. Radiant drift accounts for February mu Virginid members appearing to trace back to a point five degrees east of Iota Virginis just before the onset of the shower’s annual activity dates of mid-February to early March. The February mu Virginid shower’s radiant drift also takes in Libra the Scales and Ophiuchus the Snake Bearer constellations.

The discovery of the February mu Virginid shower was announced in the June 2013 issue of WGN, the Journal of the International Meteor Organization (IMO). Damir Šegon and five other members of the Croatian Meteor Network are credited with detecting eight new showers, including the February mu Virginids, via the Croatian Meteor Network’s 2007 to 2010 catalogues and Japan’s SonotaCo Network’s 2007 to 2011 catalogues.

Astronomer and Sky & Telescope magazine editor James Mullaney suggests another star hopping strategy for locating NGC 5634. Mullaney specifies NGC 5634’s celestial placement at three degrees west of Mu Virginis and 30 minutes east of sixth magnitude star 104 Virginis. The blue subgiant is visible to the naked eye. HLA celestial coordinates for 104 Virginis are right ascension at 14 hours 27 minutes 24.387 seconds and declination at minus 6 degrees 7 minutes 13.21 seconds. Mullaney notes the location of 104 Virginis in “the same wide eyepiece field.”

Hartmut Frommert of the University of Konstanz’s Physics Department in southwestern Germany locates NGC 5634 at a distance of 82.2 kilo-light years. Southeastern Virgo’s globular cluster lies 69.1 kilo-light years from the Milky Way’s Galactic Center. One kilo-light year approximates 63,240,000 astronomical units (AU); 9,460,528,405,000,000 kilometers; 5,878,499,814,210,000 miles.

German-British astronomer and composer Sir Frederick William Herschel (Nov. 15, 1738-Aug. 25, 1822) is credited as NGC 5634’s discoverer. He discerned southeastern Virgo’s globular cluster March 5, 1785, almost four years after his discovery of the planet Uranus. Sir Herschel’s discovery of the solar system’s seventh planet happened March 13, 1781.

NGC 5634 appears as number 70 in “I. First Class. Bright Nebulae” in Sir William’s Catalogue of One Thousand New Nebulae and Clusters of Stars (1786). In his system of abbreviated descriptions, Sir William summarized Virgo’s globular cluster (page 472): “vB. cL. iF. vgbM.” His description translates as: “very bright. considerably round. irregularly faint. very gradually brighter in the middle.”

Sir William identified 106 Virginis as the star referenced for NGC 5634’s placement. His details revealed “that the nebula is . . . following the star” by a sidereal time of 1 minute 2 seconds and at 0 degrees 54 minutes north of the “determining star.”

With an apparent magnitude of 5.42, the fifth magnitude star comes in close to sixth magnitude. HLA celestial coordinates for 106 Virginis are right ascension of 14 hours 28 minutes 41.721 seconds and declination of minus 6 degrees 54 minutes 01.89 seconds.

Sir William’s son, English astronomer and polymath Sir John Frederick William Herschel, 1st Baronet (March 7, 1792-May 11, 1871), also catalogued astronomical observations. In his 1833 catalogue, Sir John noted his observations of southeastern Virgo’s globular cluster, under entry 1813 (page 451): “A fine small compressed globular cluster. I can barely discern the stars; they are 19 m 80” diam; has a * 7.8 m 90” dist, pos 30° s f, and another 10 m, n p.”

Sir William’s catalogue entry I.70 equates to number 3900 in Sir John’s 1864 catalogue. Sir John sought to combine his and his father’s observations in an abbreviated description (page 116): “⊕; vB; cL; R; gbM; rrr; st 19; *17 sf.” His abbreviations translate as: “globular cluster of stars; very bright; considerably large; round; gradually brighter in the middle; well resolved -- clearly seen to consist of stars; stars of the 19th magnitude; star of 17th magnitude south following.”

The prefix NGC for Virgo’s lone globular cluster abbreviates New General Catalogue, a list of deep-sky objects compiled by Danish-Irish astronomer John Louis Emil Dreyer (Feb. 13, 1852-Sept. 14, 1926). Published in 1888 in the Memoirs of the Royal Astronomical Society, Dreyer’s catalogue comprises observations by Sir William; his son, Sir John; his sister, Caroline Herschel (March 16, 1750-Jan. 9, 1848); Scottish Southern Hemisphere astronomer James Dunlop (Oct. 31, 1793-Sept. 22, 1848); and other sources.

The takeaways for globular cluster NGC 5634, which lies midway between Iota and Mu Virginis in southeastern Virgo the Virgin constellation, are that its discovery is credited to German-British astronomer Sir William Herschel, the discoverer of Uranus, that naked eye stars 104, Iota and Mu Virginis star hop deep-sky observers to its location and that Virgo claims NGC 5634 as the constellation’s only globular cluster.

Located in southeastern Virgo the Virgin, NGC 5634 rates as the constellation's only globular cluster: HST (Hubble Space Telescope) Phase 2 GSC2 (Guide Star Catalog 2)/NASA and STScI (Space Telescope Science Institute), Public Domain, via STScI

Acknowledgment

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

Image credits:

Sir William Herschel’s 1785 discovery of Virgo’s only globular cluster, NGC 5634, occurred almost four years after his 1781 discovery of Uranus; 2.2 arcmin wide image of NGC 5634’s northwestern part: Hubble Legacy Archive, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:NGC_5634_Hubble_WikiSky.jpg

Located in southeastern Virgo the Virgin, NGC 5634 rates as the constellation's only globular cluster: HST (Hubble Space Telescope) Phase 2 GSC2 (Guide Star Catalog 2)/NASA and STScI (Space Telescope Science Institute), Public Domain, via STScI MAST (Barbara A. Mikulski Archive for Space Telescopes) @ http://archive.stsci.edu/cgi-bin/dss_search?v=poss2ukstu_red&r=14+29+37.28&d=-05+58+35.1&e=J2000&h=15.0&w=15.0&f=gif&c=none&fov=NONE&v3=

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