NGC 2403 is an intermediate spiral galaxy located in the faint northern constellation of Camelopardalis. This superb magnitude +8.4 object is about 10 Million light-years distant and is an outlying member of the M81 group of galaxies, which also includes M81 and M82. Since it's relatively near, and almost face-on from our perspective, NGC 2403 displays intricate details in its spiral arms especially through large amateur scopes.
NGC 2403 was discovered on November 1, 1788 by William Herschel and is best seen from northern latitudes during the months of January, February and March. It's number 7 in the Caldwell catalogue.
The galaxy is located in the southeastern corner of Camelopardalis not far from the Ursa Major and Lynx borders. In a barren region of sky, it's positioned between two 6th magnitude stars. Almost 8 degrees southeast of NGC 2403 is star Muscida (ο UMa - mag. +3.4).
The structure of NGC 2403 resembles that of M33 in Triangulum. Both galaxies are spatially similar in size, appear almost face-on from our perspective and contain numerous HII star-forming regions, although M33 is more than three times closer to us than NGC 2403.
Through 7x50 binoculars, NGC 2403 appears as a faint patch of nebulous light. With an 80mm (3.1-inch) refractor, it displays a bright core surrounded by an oval fuzz without detail. A larger 200mm (8-inch) scope reveals mottling, and on good nights part of the brighter northern spiral arm can be seen. In addition, averted vision reveals numerous bright and dark regions. On closer inspection the bright nucleus appears slightly oval shaped. In very large instruments, for example 400mm (16-inch) reflectors, the spiral arms are much easier to distinguish.
There are more than 100 known emission nebulae in NGC 2403's spiral arms with some spanning up to 800 light-years and visible in large backyard scopes. In total, the galaxy spans 21.9 x 12.3 arc minutes of apparent sky.
NGC 2403 is a wonderful spiral and is the brightest galaxy in the northern section of sky that's not included in the Messier catalogue. It has a spatial diameter of 65,000 light-years and is estimated to contain about 50 billion stars. To date, three supernovae have been reported, SN 1954J, SN 2002kg and SN 2004dj.
NGC 2403 Data Table
|Object Type||Intermediate Spiral Galaxy|
|Distance (light-years)||10 Million|
|RA (J2000)||07h 36m 51s|
|DEC (J2000)||65d 36m 09s|
|Apparent Size (arc mins)||21.9 × 12.3|
|Number of Stars||50 Billion|
|Notable Feature||Is an outlying member of the M81 Group|