Messier 12 or M12 (also designated NGC 6218) is a globular cluster in the constellation Ophiuchus. It has an apparent visual magnitude of 6.7 and its angular diameter is 14.5 arc-minutes. M12 lies at an estimated distance of 16,000 light years. The Equinox 2000 coordinates are RA= 16h 47.2m, Dec= -01° 57´ which makes M12 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 M12 through the Takahashi E-180 Astrograph (North is up). A 3x enlargement of this image appears to the right.
This globular cluster was discovered by Messier in 1764. According to Recio-Blanco et al.(2005), the distance of M12 is 20,760 light years and its diameter is 85 light years. Its estimated mass is 250,000 solar masses and it contains 5 variable stars.
Messier's Description of M12
May 30, 1764
`Nebula discovered in the Serpent, between the arm and the left side of Ophiuchus: this nebula doesn't contain any star, it is round and its light faint; near this nebula there is a star of 9th magnitude. M. Messier has reported it on the second Chart of the Comet observed in 1769. Mem. Acad. 1775, pl. IX. Reviewed March 6, 1781. (diam. 3')'
- Object: M12
- Other Names: NGC 6218
- Object Type: globular cluster
- Object Data: Apparent Magnitude = 6.7, Angular Size = 14.5 arc-minutes
- Object Position (Equinox 2000): RA= 16h 47.2m, Dec= -01° 57´, Constellation = Ophiuchus
- Date/Time: 2011 Apr 11 at 10:46 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: 2 x 300s, f/2.8, ISO 800
- File Name: M12-01w.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.