Upsilon Carinae (υ Car, υ Carinae) is a double star in the southern constellation of Carina. It is part of the Diamond Cross asterism in southern Carina. The Upsilon Carinae system has a combined apparent magnitude of +2.97 and is approximately 1,400 light years (440 parsecs) from Earth.
In Chinese, 海石 (Hǎi Dàn), meaning Sea Rock, refers to an asterism consisting of υ Carinae, ε Carinae, ι Carinae, HD 83183 and HD 84810. Consequently, υ Carinae itself is known as 海石五 (Hǎi Dàn wǔ, English: the Fifth Star of Sea Rock.)
The primary component, υ Carinae A, has a stellar classification of A8 Ib, making it a supergiant star that has exhausted the hydrogen at its core and evolved away from its brief main sequence lifetime as a O9 V star. With an apparent magnitude of +3.08, it has an effective temperature of about 7,600 K, giving it a white hue. The companion, υ Carinae B, is a giant star with a classification of B7 III, although Mandrini and Niemela (1986) suggested it may be a subgiant star with a classification of B4–5 IV. The outer envelope of this star has an effective temperature of around 23,000 K, resulting in the blue-white hue of a B-type star.
The two stars have an angular separation of 5.030 arcseconds. As a binary star system, they would have an estimated orbital period of at least 19,500 years and a present day separation of around 2,000 Astronomical Units. This system is roughly 12 million years old.