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VY Canis Majoris
VY Canis Majoris (VY CMa) is a red hypergiant star located in the constellation Canis Major. It is one of the largest stars (at one time it was the largest known) and also one of the most luminous of its type, and has a radius of approximately 1,420 ± 120 solar radii (equal to a diameter of 13.2 astronomical units, or about 1,976,640,000 km), and is located about from Earth.
VY Canis Majoris is a single star categorized as a semiregular variable with an estimated period of 2,000 days. It has an average density of 5 to 10 mg/m3. If placed at the center of the Solar System, VY Canis Majoris's surface would extend beyond the orbit of Jupiter, although there is still considerable variation in estimates of the radius.
==Observational history==
The first known recorded observation of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on 7 March 1801, which lists it as a 7th magnitude star. Further 19th-century studies of its apparent magnitude demonstrate that the star has been fading since 1850. Since 1847, VY Canis Majoris has been described as a crimson star.〔 During the 19th century, observers measured at least six discrete components, suggesting that it might be a multiple star. These discrete components are now known to be bright areas in the surrounding nebula. Visual observations in 1957 and high-resolution imaging in 1998 showed that there are no companion stars.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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