U Geminorum (U Gem), in the constellation Gemini, is an archetypal example of a dwarf nova.

U Geminorum was discovered by J.R. Hind in 1855 who initially thought it was a nova; it quickly faded below his telescope's limiting magnitude.

[10] The star has been monitored by amateur and professional astronomers ever since, though its location near the zodiac means that some outbursts are undoubtedly missed due to the seasonal gap.

The orbital motion of the two stars causes their spectral lines to shift due to the doppler effect.

However, the wavelengths of the white dwarf spectral lines are also changed due to its gravitational redshift.