Messier 75 or M75 (also designated NGC 6864) is a globular cluster in the constellation Sagittarius. It has an apparent visual magnitude of 8.5 and its angular diameter is 6 arc-minutes. M75 lies at an estimated distance of 61,300 light years. The Equinox 2000 coordinates are RA= 20h 06.1m, Dec= -21° 55´ which makes M75 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 M75 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 M75 is 77,840 light years and its diameter is 160 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. Its estimated mass is 500,000 solar masses and it contains 46 variable stars.
Messier's Description of M75
October 18, 1780
`Nebula without star, between Sagittarius and the head of Capricorn; seen by M. Méchain on August 27 and 28, 1780. M. Messier looked for it on the following October 5, and on October 18, compared it [i.e., its position] with the star 4 Capricorni, of sixth magnitude, according to Flamsteed: it seemed to M. Messier to be composed of nothing but very small [faint] stars, containing nebulosity: M. Méchain reported it as a nebula without stars. M. Messier saw it on October 5; but the Moon being above the horizon, and it was not until the 18th of the same month that he was able to judge about its form and determine its position.'
- Object: M75
- Other Names: NGC 6864
- Object Type: globular cluster
- Object Data: Apparent Magnitude = 8.5, Angular Size = 6 arc-minutes
- Object Position (Equinox 2000): RA= 20h 06.1m, Dec= -21° 55´, Constellation = Sagittarius
- Date/Time: 2011 Oct 19 at 03:34 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: 8 x 300s, f/2.8, ISO 800
- File Name: M75-01w.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.