29 Canis Majoris is a star in the constellation Canis Major. It is classified as a Beta Lyrae eclipsing contact binary and given the variable star designation UW CMa. Its brightness varies from magnitude +4.84 to +5.33 with a period of 4.39 days.
29 Canis Majoris A is a rare O-type blue supergiant, while its companion is a slightly less evolved and less luminous O-type star. Parallax measurements showed it to be approximately 3000 light years from Earth, but this is unexpectedly close for a star of its spectral type and brightness. Recent more accurate Hipparcos parallax data gives an even closer result around 2000 light years. It is thought to be distant member of NGC 2362 which would place it about 5000 light years and more closely match its expected luminosity. The contradiction between the different distance results is still a subject of research.