От википедията:
Comet Holmes not only became brighter, but it also swelled in size as its coma expanded. In late October 2007 the coma's apparent diameter increased from 3.3 arcminutes to over 13 arcminutes, about half the diameter of the Moon in the sky. At a distance of around 2 AU, this means that the true diameter of the coma had swelled to over 1 million km, or about 70% of the diameter of the Sun. By comparison, the Moon is 380,000 km from Earth. Therefore, during the 2007 outburst of Comet Holmes the coma was a sphere wider than the diameter of the Moon's orbit around Earth. In November 2007, the coma had dispersed to a volume larger than the Sun, briefly giving it the largest extended atmosphere in the Solar System.