Omicron Velorum (ο Vel, ο Velorum) is a star in the constellation Vela. It is the brightest member of the loose naked eye open cluster IC 2391, also known as the ο Velorum Cluster. Omicron Velorum is a blue-white B-type star with a mean apparent magnitude of +3.60. It is probably a main sequence object, but has also been classified as a subgiant or giant. It is approximately 495 light years from Earth. A slowly pulsating B star, it ranges between magnitudes 3.57 and 3.63 over 2.8 days. The correct Bayer designation for ο Velorum has been debated. Lacaille assigned one Greek letter sequence for the bright stars of Argo Navis. These Lacaille designations are now shared across the three modern constellations of Carina, Puppis, and Vela so that (except for omicron) each Greek letter is found in only one of the three. However, ο (omicron) is now commonly used for two stars, one each in Vela and Puppis. In the Coelum Australe Stelliferum itself, ο Velorum is labelled ο (omicron) Argus (du Navire in the French edition), while ο Puppis is labelled (Latin) o Argus in puppi (Pouppe du Navire in the French edition). Some later authors state the reverse, that Lacaille actually assigned omicron to ο Puppis and Latin lower case 'o' to ο Velorum. . Modern catalogs and atlases generally use omicron for both stars.