# NGC 6624

NGC 6624
The globular cluster NGC 6624. Credit Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationSagittarius
Right ascension18h 23m 41s
Declination−30° 21′ 39″
Distance25.8 ± 1.1 kly (7.91 ± 0.34 kpc)
Apparent magnitude (V)7.6
Apparent dimensions (V)8.8 arcminutes[1]
Physical characteristics
Metallicity${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = -0.56 ± 0.27[2] dex
Other designationsESO 457-11, GCl 93, CD−30 15631, CPD−30 5486, HD 168943[3]
See also: Globular cluster, List of globular clusters

NGC 6624 is a globular cluster in the constellation Sagittarius. It was discovered on 24 June 1784 by the astronomer William Herschel. It is given an apparent magnitude of 7.6 to 8.5.[4] Six pulsars are known in NGC 6624. The first of these to be discovered was PSR J1823-3021A. This globular cluster also contains 4U 1820-30, a low-mass X-ray binary with an orbital period of only 11.5 minutes.

NGC 6624 is visible as a hazy spot with a small telescope, and appears as a star-like object with binoculars. Its core appears significantly condensed.[1] It is located 0.8 degrees southeast of the star Delta Sagittarii,[5] and is about 1.17 kpc (3.8 kly) from the Galactic center.[2]

Map showing location of NGC 6624

## References

1. ^ a b O'Meara, Steve (2007). Steve O'Meara's Herschel 400 Observing Guide. Cambridge: Cambridge University Press. p. 236. ISBN 978-0-521-85893-9.
2. ^ a b Sofue, Yoshiaki (1998-08-31). The Central Regions of the Galaxy and Galaxies. Netherlands: Kluwer Academic Publishers. p. 37. ISBN 978-0-7923-5061-3.
3. ^ "NGC 6624". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-02-19.
4. ^ It is given a diameter of 6 to 8.5 arcminutes, and class VI with stars magnitude 14 and dimmer. It is less than a degree southeast of star Delta Sagittarii. O'Meara, Stephen James (2007). Deep Sky Companions: Hidden Treasures. Cambridge University Press. p. 452. ISBN 978-1-139-46373-7.
5. ^ Bakich, Michael E. (2010). 1001 Celestial Wonders to See Before You Die: The Best Sky Objects for Star Gazers. Patrick Moore's Practical Astronomy Series. Springer. p. 249. doi:10.1007/978-1-4419-1777-5. ISBN 978-1-4419-1776-8.
• Robert Burnham, Jr, Burnham's Celestial Handbook: An observer's guide to the universe beyond the solar system, vol 3, p. 1557