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Though relatively young in stellar terms (probably less than twenty million years old), Omicron1 Canis Majoris is a massive star that has burned through its hydrogen and is now fusing helium in its core. In the process it has expanded to become a supergiant so huge that, if lay at the centre of the Solar System, its outer shell would lie beyond the orbit of Mars. It is some ten thousand times more luminous than the Sun in visual wavelengths.

Omicron1 Canis Majoris is part of a group of stars in central Canis Major that belong to the loose cluster designated Collinder 121. Other prominent stars that are likely members of this group include Muliphein, Wezen and Unurgunite (Gamma, Delta and Sigma Canis Majoris, respectively). A less prominent member is the faint variable EZ Canis Majoris which is surrounded by a bubble of nebulous material. EZ Canis Majoris is a close neighbour to Omicron1 Canis Majoris in space, to the extent that the supergiant appears to interact with the expanding gases of the bubble nebula.

The star almost directly northward of Omicron1 Canis Majoris is the hot Wolf-Rayet star EZ Canis Majoris, surrounded by a faint bubble nebula. The arc of this nebula can be seen extending outward as far as Omicron1, which appears to interact with its expanding gases. Imagery provided by Aladin sky atlas

Omicron1 Canis Majoris is a very distant star, lying so far away that its precise distance is difficult to calculate. Early estimates placed it 2,000 light years or more from the Solar System, but more recent parallax data suggests that it is a little closer than this, and probably falls some 1,300 light years from the Sun.


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