largest star

The largest star certainly belongs to the class of red supergiants, though the difficulty of measuring precise sizes for most stars means it is not possible to say for certain which is the largest. These stars as a group have radii which are comparable with the orbits of Jupiter or Saturn in the solar system - from 800 to 1,600 million kilometres, or between 1200 and 2400 times the size of the Sun. A possible candidate for the largest star is Alpha Herculis. Another very large red supergiant is Mu Cephei. Red supergiants are stars in a late stage of evolution. When the hydrogen fuelling the nuclear energy source at the star's centre begins to run out, a stage in the interior changes that take place causes the outer layers of the star to expand greatly. A red supergiant consists of a huge envelope of very tenuous gas around the central core of the star.