NGC 2403 is an intermediate spiral galaxy in the constellation Camelopardalis. It has a H II nucleus. It was discovered by William Herschel in 1788. NGC 2403 is an outlying member of the M81 Group, and is approximately 8 million light-years distant. The northern spiral arm connects to NGC 2404. It may be easily seen using 10 ? 50 binoculars.
Allan Sandage detected Cepheid variables in NGC 2403 using the Hale telescope, making it the first galaxy beyond our local group to have Cepheids found in it. He derived a distance of a mere 8 kly. Today, it is thought to be a thousand times further away at about 8 Mly (3.6 Mpc).