Globular Cluster NGC 6717

NGC 6717
NGC 6717: Image taken with Hubble Space Telescope. © 2021 ESA/Hubble and NASA, A. Sarajedini [636]


This globular cluster was discovered by William Herschel on 7 August 1784 using his reflector of 18.7 inch aperture and 20 feet focal length. As he could not resolve the cluster he cataloged it as «very faint nebula» with III 143 and noted: «Three very small stars with suspected nebulosity.» [463] His son John observed the cluster on 1st July 1826 with his 18.25 inch reflector with 20 feet focal length, located in Slough. He cataloged it as h 2022 and noted: «A little knot of 8 or 10 stars crowded together. It is 1' 40" south of ν2 Sagittarii, and on same meridian.» [466] Few years later on 27 June 1837 during his stay in Feldhausen, South Africa, he observed the cluster again and cataloged it as h 3766 with the notes: «Close to the south of ν2 Sagittarii; a very small clustering knot, with perhaps nebula. A doubtful object. I see 3 or 4 of the stars, but there is also a nebulous appearance.» [11]

On 30 June 1884 the French astronomer Guillaume Bigourdan thought he found a «nebulosity around stars of 13 magnitudes, 15" north following III 143» and cataloged it as B 434. In 1888 John L. E. Dreyer added Herschel's object with NGC 6717 as «cluster with nebulosity» to his «New General Catalogue». [313] Bigourdans object was added later in 1912 as IC 4802 in the «Second Index Catalogue» [316]

In the 1950s the cluster was identified as a globular cluster by the American astronomer George Ogden Abell on photo plates from the Palomar Observatory Sky Survey. He was cataloged as Palomar 9. [331]

Physical Properties

NGC 6717 is located at a distance of 7.1 kpc from the Sun and 2.4 kpc from the Galactic centre, which places it in the bulge of the Milky Way. It has a dense core, which may indicate that it has undergone a core collapse. [148]

Revised+Historic NGC/IC Version 22/9, © 2022 Dr. Wolfgang Steinicke [277]
Name RA Dec Type bMag vMag B-V SB Dim PA z D(z) MD Dreyer Description Identification, Remarks
NGC 6717 18 55 06.2 -22 42 01 GCL (VIII) 8.4 5.4 7.100 F, S, rr, Cl + neb WH III 143; h 2022=3766; GC 4444; Pal 9; GCL 105; ESO 523-SC14
IC 4802 18 55 07.2 -22 41 51 *Grp Neb * 13, 15" nf III 143 in GCL N 6717=Pal 9

Finder Chart

The globular cluster is located in the constellation Sagittarius and the best time for observing is from May to September.

Finder Chart Globular Cluster NGC 6717
Globular Cluster NGC 6717 in constellation Sagittarius. Charts created using SkySafari 6 Pro and STScI Digitized Sky Survey. Limiting magnitudes: Constellation chart ~6.5 mag, DSS2 close-ups ~20 mag. [149, 160]

Objects Within a Radius of 15°


  • [11] «Results of astronomical observations made during the years 1834, 5, 6, 7, 8, at the Cape of Good Hope ... : being the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825» Herschel, John F. W.; London : published by Smith, Elder and Co., 1847; DOI:10.3931/e-rara-22242
  • [148] «A Catalog of Parameters for Globular Clusters in the Milky Way» Harris, William E.; Astronomical Journal v.112, p.1487, October 1996 / Revision: December 2010; DOI:10.1086/118116; Bibcode:1996AJ....112.1487H; (2021-01-03)
  • [149] SkySafari 6 Pro, Simulation Curriculum;
  • [160] The STScI Digitized Sky Survey;
  • [277] «Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)
  • [313] «A New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel, Bart., revised, corrected, and enlarged» Dreyer, J. L. E. (1888); Memoirs of the Royal Astronomical Society. 49: 1–237; Bibcode:1888MmRAS..49....1D
  • [316] «Corrections to the New General Catalogue resulting from the revision of Sir William Herschel's Three Catalogues of Nebulae» Dreyer, J. L. E. (1912); Monthly Notices of the Royal Astronomical Society. 73: 37–40.; DOI:10.1093/mnras/73.1.37; Bibcode:1912MNRAS..73...37D
  • [331] «Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey» Abell, G. O.; Publications of the Astronomical Society of the Pacific, Vol. 67, No. 397, p.258-261, August 1955; DOI:10.1086/126815; Bibcode:1955PASP...67..258A
  • [463] «Catalogue of one thousand new nebulae and clusters of stars» William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1786; DOI:10.1098/rstl.1786.0027
  • [466] «Observations of nebulæ and clusters of stars, made at Slough, with a twenty-feet reflector, between the years 1825 and 1833» John Frederick William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1833, Pages: 359-505; DOI:10.1098/rstl.1833.0021
  • [636] A Glittering Globular Cluster; (2023-09-08)