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 | = –1.48 ± 0.03 [3] dex |
Estimated age | 9.5 Gyr [6] |
Other designations | NGC 6981, GCl 118 [7] |
Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the very mildly southern constellation of Aquarius.
M72 was discovered by astronomer Pierre Méchain in 1780. [a] 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. The surrounding field stars become visible from a 15 cm (5.9 in)-aperture device. One of 25 cm (9.8 in) will allow measurement of an angular diameter of 2.5 ′. At 30 cm (12 in) the core is clear: its 1.25 ′ diameter, meaning a broad spread; and small parts scarcer in stars to the south and east. [10]
Based upon a 2011 census of variable stars, the cluster is 54.57 ± 1.17 kly (16.73 ± 0.36 kpc) away from the Sun. [3] It has an estimated combined mass of 168,000 [5] solar masses (M☉) and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times solar luminosity (L☉) per cubic parsec. [6] There are 43 identified variable stars in the cluster. [3]
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 | = –1.48 ± 0.03 [3] dex |
Estimated age | 9.5 Gyr [6] |
Other designations | NGC 6981, GCl 118 [7] |
Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the very mildly southern constellation of Aquarius.
M72 was discovered by astronomer Pierre Méchain in 1780. [a] 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. The surrounding field stars become visible from a 15 cm (5.9 in)-aperture device. One of 25 cm (9.8 in) will allow measurement of an angular diameter of 2.5 ′. At 30 cm (12 in) the core is clear: its 1.25 ′ diameter, meaning a broad spread; and small parts scarcer in stars to the south and east. [10]
Based upon a 2011 census of variable stars, the cluster is 54.57 ± 1.17 kly (16.73 ± 0.36 kpc) away from the Sun. [3] It has an estimated combined mass of 168,000 [5] solar masses (M☉) and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times solar luminosity (L☉) per cubic parsec. [6] There are 43 identified variable stars in the cluster. [3]