Messier 46 or M46 (also designated NGC 2437) is an open cluster in the constellation Puppis. It has an apparent visual magnitude of 6 and its angular diameter is 27 arc-minutes. M46 lies at an estimated distance of 5400 light years. The Equinox 2000 coordinates are RA= 7h 41.8m, Dec= -14° 49´ which makes M46 best seen during the winter. The Messier Winter Star Chart shows the position of all Messier objects visible during that season.
The image above shows the uncropped view of M46 through the ASA N12 Corrected Newtonian Astrograph (North is to the right). The bright star HR 2959 (magnitude 4.96) is about 0.5 degree southwest of M46 (lower left corner).
One of the most noteworthy features of M46 is the planetary nebula NGC 2438 appearing 7 arc-minutes northeast of the cluster's center. The planetary is believed to be a foreground object and not physically associated with the cluster. A 3x enlargement of the above image centered on NGC 2438 appears to the right.
The open cluster M46 was discovered by Messier in 1771. According to Kharchenko et al. (2005), the distance of M46 is 4480 light years and its diameter is 26 light years. It contains 500 stars and its estimated age is 500 million years.
Messier's Description of M46
February 19, 1771
`A cluster of very small stars, between the head of the Great Dog and the two hind feet of the Unicorn, [its position] determined by comparing this cluster with the star 2 Navis, of 6th-magnitude, according to Flamsteed; one cannot see these stars but with a good refractor; the cluster contains a bit of nebulosity.'
- Object: M46
- Other Names: NGC 2437
- Object Type: open cluster
- Object Data: Apparent Magnitude = 6, Angular Size = 27 arc-minutes
- Object Position (Equinox 2000): RA= 7h 41.8m, Dec= -14° 49´, Constellation = Puppis
- Date/Time: 2012 Mar 15 at 04:22 UTC
- Location: Bifrost Astronomical Observatory, Portal, AZ
- Mount: Astro-Physics 1200GTO
- Telescope: ASA N12 Corrected Newtonian Astrograph
- Camera: Canon EOS 550D (Rebel T2i) (modified with a Baader UV/IR filter)
- Field of View: 71.0 x 47.4 arc-minutes at 0.82 arc-sec/pixel (web version: 4.6 arc-sec/pixel)
- Exposure: 4 x 120s, f/3.6, ISO 800
- File Name: M46-A01w.jpg
- Processing (Adobe Camera Raw): Flat Field Subtraction, Noise Reduction, White Balance
- Processing (Photoshop CS5): Average Images, Curves, Noise Reduction, High Pass Filter, Unsharp Mask
- Original Image Size: 3454 × 5179 pixels (17.9 MP); 11.5" x 17.3" @ 300 dpi
- Rights: Copyright 2012 by Fred Espenak. All Rights Reserved. See: Image Licensing.