Messier 73 or M73 (also designated NGC 6994) is an Asterism in the constellation Aquarius. It has an apparent visual magnitude of 9 and its angular diameter is 2.8 arc-minutes. The four stars making up M73 lie over a range of distances from about 900 to 2600 light years. The Equinox 2000 coordinates are RA= 20h 59m, Dec= -12° 38´ which makes M73 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 M73 through the Takahashi E-180 Astrograph (North is to right). A 3x enlargement of this image appears to the right.
M73 is a conspicuous asterism consisting of four stars. It was discovered by Messier in 1780. According to Stoyan et al. (2010), the distance of the stars in M73 range from 900 to 2590 light years.
Messier's Description of M73
October 4 and 5, 1780
`Cluster of three or four small stars, which resembles a nebula at first sight, containing a little nebulosity: this cluster is situated on the same parallel as the preceding nebula [M72]: its position was determined from the same star Nu Aquarii.'
in Messier's handwritten notes on the discovery of the objects, he does not mention Nu Aquarii, and his description on how he measured M72 implies that this "Same Star" may actually be 6th-mag HD 198431 just west of M72.)
- Object: M73
- Other Names: NGC 6994
- Object Type: Asterism
- Object Data: Apparent Magnitude = 9, Angular Size = 2.8 arc-minutes
- Object Position (Equinox 2000): RA= 20h 59m, Dec= -12° 38´, Constellation = Aquarius
- Date/Time: 2011 Nov 02 at 09:07 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: M74-01w.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.