Messier 72 or M72 (also designated NGC 6981) is a globular cluster in the constellation Aquarius. It has an apparent visual magnitude of 9.3 and its angular diameter is 5.9 arc-minutes. M72 lies at an estimated distance of 55,400 light years. The Equinox 2000 coordinates are RA= 20h 53.5m, Dec= -12° 32´ which makes M72 best seen during the summer. The Messier Summer Star Chart shows the position of all Messier objects visible during that season.
The image above shows the uncropped view of M72 through the Takahashi E-180 Astrograph (North is to right). A 3x enlargement of this image appears to the right.
This globular cluster was discovered by P. Méchain in 1780. According to Recio-Blanco et al.(2005), the distance of M72 is 58,510 light years and its diameter is 100 light years. This makes it one of the more remote globular clusters in the Messier Catalog as it lies a good distance beyond the galactic center of the Milky Way. The estimated mass of M72 is 200,000 solar masses and it contains 51 variable stars most of them of the RR Lyrae type.
Messier's Description of M72
October 4, 1780
`Nebula seen by M. Méchain in the night of August 29-30, 1780, above the neck of Capricorn. M. Messier looked for it on the 4th and 5th October following: the light is as faint as for the preceding [M71]; near it is a small telescopic star: the position was determined from the star Nu Aquarii, of fifth magnitude.' (diam 2')
- Object: M72
- Other Names: NGC 6981
- Object Type: globular cluster
- Object Data: Apparent Magnitude = 9.3, Angular Size = 5.9 arc-minutes
- Object Position (Equinox 2000): RA= 20h 53.5m, Dec= -12° 32´, Constellation = Aquarius
- Date/Time: 2011 Oct 19 at 04:27 UTC
- Location: Bifrost Astronomical Observatory, Portal, AZ
- Mount: Astro-Physics 1200GTO
- Telescope: Takahashi Epsilon 180 Hyperbolic Astrograph
- Camera: Canon EOS 550D (Rebel T2i) (modified with a Baader UV/IR filter)
- Field of View: 1.70° x 2.56° at 1.7 arc-sec/pixel (web version: 10.0 arc-sec/pixel)
- Exposure: 4 x 300s, f/2.8, ISO 800
- File Name: M72-01w.jpg
- Processing (Adobe Camera Raw): Graduated Filter, Vignetting Correction, Noise Reduction, White Balance, Curves
- Processing (Photoshop CS5): Average Images, Curves, Noise Reduction
- Original Image Size: 3454 × 5179 pixels (17.9 MP); 11.5" x 17.3" @ 300 dpi
- Rights: Copyright 2011 by Fred Espenak. All Rights Reserved. See: Image Licensing.