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| NGC 6397 | |
|---|---|
 A Hubble Space Telescope (HST) image of NGC 6397 | |
| Observation data (J2000 epoch) | |
| Class | IX[1] |
| Constellation | Ara |
| Right ascension | 17h 40m 42.09s[2] |
| Declination | –53° 40′ 27.6″[2] |
| Distance | 7.8 kly (2.4 kpc)[3] |
| Apparent magnitude (V) | +6.68[4] |
| Apparent dimensions (V) | 32.0′ |
| Physical characteristics | |
| Mass | 1.14×105[5] M☉ |
| Radius | 34 ly[6] |
| VHB | 14.2 |
| Metallicity | = –1.76[7] dex |
| Estimated age | 13.4 ± 0.8 Gyr[8] |
| Notable features | Second closest globular cluster |
| Other designations | GCl 74,[4] Lacaille III.11, Dunlop 366, Bennett 98, Caldwell 86 |
![{\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4c0821bd80891e071c08e7c7ee8e022baedf522c)
NGC 6397 (also known as Caldwell 86) is a globular cluster in the constellation Ara that was discovered by French astronomer Nicolas-Louis de Lacaille in 1752.[9] It is located about 7,800 light-years from Earth,[3] making it one of the two nearest globular clusters to Earth (the other one being Messier 4). The cluster contains around 400,000 stars,[8] and can be seen with the naked eye under good observing conditions.[10]
NGC 6397 is one of at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse,[8] meaning that the core has contracted to a very dense stellar agglomeration.
- ^ Cite error: The named reference
hcob849_11was invoked but never defined (see the help page). - ^ a b Cite error: The named reference
aj140_6_1830was invoked but never defined (see the help page). - ^ a b Salazar, Doris Elen (5 April 2018). "Cosmic 'Yardstick' Measures Distance to One of Universe's Oldest Objects". Space.com. Retrieved 5 April 2018.
- ^ a b Cite error: The named reference
simbadwas invoked but never defined (see the help page). - ^ Cite error: The named reference
Vitral+22was invoked but never defined (see the help page). - ^ distance × sin( diameter_angle / 2 ) = ~34 ly. radius
- ^ Cite error: The named reference
mnras404_3_1203was invoked but never defined (see the help page). - ^ a b c Cite error: The named reference
esowas invoked but never defined (see the help page). - ^ Jones, K. G. (March 1969). "The search for the nebulae - VI". Journal of the British Astronomical Association. 79: 213–222. Bibcode:1969JBAA...79..213J.
- ^ Dunlop, Storm (2005). Atlas of the Night Sky. Collins. ISBN 978-0-00-717223-8.