What Is the Largest Star?

Size comparison between the Sun and VY Canis Majoris.

Owing to the physical difficulties in directly measuring the size of a distant star, the identity of the largest star is a matter for debate among astronomers. The current most likely candidate is VY Canis Majoris, a red supergiant some 5,000 light years away. Estimates of its size give it a diameter of 2.5 – 3 billion km (1.55 – 1.86 billion miles), or 1,800 – 2,100 times that of the Sun.

If placed at the centre of the Solar System, the star’s outer surface would reach beyond the orbit of Jupiter. Some astronomers disagree, and think that VY Canis Majoris might be smaller; merely 600 times the size of the Sun, extending past the orbit of Mars.

The first known record of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on March 7, 1801. The catalogue listed VY CMa as a 7th magnitude star. Further studies on its apparent magnitude during the 19th century showed that the star has been fading since 1850.