Globular Cluster NGC 6624

NGC 6624
NGC 6624: Image taken with Hubble Space Telescope. © 2006 STScI [177]


This globular cluster was discovered by William Herschel on 24 June 1784 using his 18.7 inch reflector. He could not resolve the cluster and cataloged it with I 50 as a bright nebula with the notes: «Considerably large, round, very brighter in the middle, milky.» [463] John Herschel identified the object as a globular cluster in 1832, but could barely resolve it with his 20 feet telescope with 18.3 inch aperture in Slough. [466] Later in 1835 from Feldhausen on the Cape of Good Hope he could clearly resolve the globular cluster into stars and named it «a fine object». [11]

Physical Properties

NGC 6624 is a globular cluster located in the bulge close to the galactic centre. Its distance from the Sun is 8.0 ± 0.1 kpc and from the galactic centre is 1.2 kpc. The cluster shows a cusp in the stellar distribution of the central regions which is typical for systems that have undergone a core collapse.

This globular cluster hosts many known pulsars, some of which are millisecond pulsars that have a short characteristic age. This is contrary to the usual scenario of pulsar formation. Globular clusters usually host very old stars and show no signs of star formation, so no massive stars were around to form these pulsars. These pulsars are thought to be old neutron stars that encountered other stars in this dense cluster and started moving by accreting matter from their new companions. [606]

Revised+Historic NGC/IC Version 22/9, © 2022 Dr. Wolfgang Steinicke [277]
Designation NGC 6624
Type GCL (VI)
Right Ascension (J2000.0) 18h 23m 40.5s
Declination (J2000.0) -30° 21' 38"
Diameter 8.8 arcmin
Visual magnitude 7.6 mag
Metric Distance 7.900 kpc
Dreyer Description globular, vB, pL, R, rrr, st 16
Identification, Remarks WH I 50; h 3742; GC 4404; GCL 93; ESO 457-SC11

Finder Chart

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

Finder Chart Globular Cluster NGC 6624
Globular Cluster NGC 6624 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
  • [149] SkySafari 6 Pro, Simulation Curriculum;
  • [160] The STScI Digitized Sky Survey;
  • [177] Hubble Legacy Archive; (2021-01-02)
  • [277] «Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)
  • [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
  • [606] «Four pulsar discoveries in NGC 6624 by TRAPUM using MeerKAT» F Abbate, A Ridolfi, E D Barr, S Buchner, M Burgay, D J Champion, W Chen, P C C Freire, T Gautam, J M Grießmeier, L Künkel, M Kramer, P V Padmanabh, A Possenti, S Ransom, M Serylak, B W Stappers, V Venkatraman Krishnan, J Behrend, R P Breton, L Levin, Y Men; Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 2, June 2022, Pages 2292–2301; DOI:10.1093/mnras/stac1041