How big is the largest star known compared to the Sun?

The biggest star I know in physical size is the supergiant star Mu Cephi about 1800 light years distant, and believed to have a surface that extends past the orbit of Saturn if placed in our solar system. The bright star Betelgeuse in Orion (shown above in a Hubble Space Telescope image) is about 1000 times the radius of the Sun, with an outer surface that would be out past the orbit of Jupiter.

The most massive star I know about is the 'pistol star' near the center of our Milky Way galaxy over 28,000 light years away, which was spotted by the Hubble Space Telescope. The image above shows this bright star embedded in a nebulosity, which is probably its own mass that is being ejected into space by the pressure of the stars own light!

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