Omicron1 Centauri (ο1 Cen, ο1 Centauri) is a star in the constellation Centaurus. It is approximately 10,000 light years from Earth, though this is very uncertain. ο1 Centauri is a yellow G-type supergiant or hypergiant with a mean apparent magnitude of +5.13. It is classified as a semiregular variable star and its brightness varies from magnitude +5.8 to +6.6 with a period of 200 days. Other studies have reported only small brightness variations. It is the MK spectral standard for class G3 O-Ia, indicating a highly luminous mass-losing hypergiant star. It has also be classified as F8 Ia0 and F7 Ia/ab. The size, luminosity, and distance are equally uncertain. ο1 Cen forms a very close naked eye double star with ο2 Centauri, a hotter blue supergiant that may be physically associated. ο1 Cen also has an 11th magnitude companion only 13.5" distant, although it appears to be a foreground star unrelated to the other two. ο1 Cen is located very close to V382 Carinae, the brightest yellow hypergiant star in the night sky.