Messier 70 or M70 (also designated NGC 6681) is a globular cluster in the constellation Sagittarius. It has an apparent visual magnitude of 7.9 and its angular diameter is 7.8 arc-minutes. M70 lies at an estimated distance of 29,400 light years. The Equinox 2000 coordinates are RA= 18h 43.2m, Dec= -32° 18´ which makes M70 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 M70 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 Messier in 1780. According to Recio-Blanco et al.(2005), the distance of M70 is 34,770 light years and its diameter is 80 light years. Its estimated mass is 200,000 solar masses and it contains at least 10 variable stars.
Messier's Description of M70
August 31, 1780
`Nebula without star, near the preceding [M69], and on the same parallel: near it is a star of the nineth magnitude and four small telescopic stars, almost on the same straight line, very close to one another, and [they] are situated above the nebula, as seen in a reversing telescope; the [position of the] nebula was determined from the same star Epsilon Sagittarii.' (diam 2')
- Object: M70
- Other Names: NGC 6681
- Object Type: globular cluster
- Object Data: Apparent Magnitude = 7.9, Angular Size = 7.8 arc-minutes
- Object Position (Equinox 2000): RA= 18h 43.2m, Dec= -32° 18´, Constellation = Sagittarius
- Date/Time: 2011 Oct 20 at 02:14 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: M70-01w.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.