Pinwheel Galaxy (M101, NGC 5457), combined optical and ultraviolet (UV) image. The ultraviolet areas (blue), mainly seen in the galactic spiral arms, show the presence of newly-formed stars (only a few million years old). The faint green light that is also seen in the spiral arms, marks stars that are more than 100 million years old. The orange glow of the centre of the galaxy shows that these stars are over a billion years old. This shows how UV astronomy can reveal stellar evolution within a galaxy. M101 is over 170,000 light years across. Ursa Major. UV data obtained by the GALEX satellite in 2003.
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