Messier 72
Globular cluster in the constellation Aquarius
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Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the southern constellation of Aquarius.
| Messier 72 | |
|---|---|
M72 from Hubble Space Telescope; 3.44′ view | |
| Observation data (J2000 epoch) | |
| Class | IX[1] |
| Constellation | Aquarius |
| Right ascension | 20h 53m 27.70s[2] |
| Declination | –12° 32′ 14.3″[2] |
| Distance | 54.57 ± 1.17 kly (16.73 ± 0.36 kpc)[3] |
| Apparent magnitude (V) | 9.3[4] |
| Apparent dimensions (V) | 6.6' |
| Physical characteristics | |
| Mass | 1.68×105[5] M☉ |
| Metallicity | [Fe/H] = –1.48 ± 0.03[3] dex |
| Estimated age | 9.5 Gyr[6] |
| Other designations | NGC 6981, GCl 118[7] |
Observational history
M72 was discovered by astronomer Pierre Méchain on August 29 1780. His countryman Charles Messier looked for it 36 days later, and included it in his catalog.[8] Both opted for the then-dominant of the competing terms for such objects, considering it a faint nebula rather than a cluster. With a larger instrument, astronomer John Herschel called it a bright "cluster of stars of a round figure". Astronomer Harlow Shapley noted a similarity to Messier 4 and 12.[9]
It is visible in a good night sky as a faint nebula in a telescope with a 6 cm (2.4 in) aperture.
Properties
Based upon a 2011 census of variable stars, the cluster is 54,500 light-years (16,700 pc) away from the Sun.[3] It has an estimated combined mass of 168,000 solar masses (M☉),[5] and is around 9.5 billion years old.[6] There are 43 identified variable stars in the cluster.[3]
