NGC 2403, cataloged as Caldwell 7, is a bright spiral galaxy in Camelopardalis that rewards astrophotographers with its sprawling, well-resolved spiral arms and numerous pink star-forming regions. At magnitude 8.38 it is one of the more accessible galaxies for imagers, though its fairly diffuse surface brightness of 21.4581 mag/arcsec² means dark skies and generous integration time bring out the faint outer disk. Spanning 10′ × 5.9′ on the sky, it frames beautifully in most deep-sky telescope and astrograph setups while leaving room for surrounding field stars. Narrowband or RGB data emphasizing hydrogen-alpha will dramatically highlight the galaxy’s many glowing emission nebulae scattered along the arms.
Names and Catalog numbers
- C 7 (Caldwell 7)
- NGC 2403
- UGC 3918
- PGC 21396
Position and the cosmic neighborhood
NGC 2403 sits in the far-northern constellation Camelopardalis at right ascension 07h 36m 51.3s and declination +65° 36′ 10″, placing it high in the sky for northern-hemisphere observers and making it favorable for long imaging sessions with minimal atmospheric distortion. Its circumpolar position from mid-northern latitudes allows it to be photographed across many months of the year. As a member of the nearby M81 group of galaxies, it lies among some of the closest galactic companions to our own Local Group, offering imagers a richly detailed, relatively undistorted view of a face-on spiral disk.
Nice to Know
- Despite its prominence, NGC 2403 carries no popular nickname and is best known simply as Caldwell 7, the seventh entry in Sir Patrick Moore’s Caldwell catalog.
- Lying just about 10.1 million light-years away, it is one of the nearest galaxies beyond the Local Group, which makes its star-forming regions exceptionally easy to resolve in amateur images.
- Its physical diameter of roughly 29,900 light-years makes it a comparatively modest spiral, yet its proximity gives it a generous 10′ × 5.9′ apparent footprint on the sky.
- The galaxy is dotted with vivid hydrogen-alpha emission nebulae, making it a superb target for narrowband and RGB imaging that captures its pink stellar nurseries.
Brightness, distance and size
The object has an apparent magnitude of 8.4 mag, it lies about 10.1 million light-years from Earth and spans roughly 29,900 light-years across. On the sky it appears about 10′ × 5.9′ in size.
