Pinwheel galaxy. Optical image of the Pinwheel galaxy (M33) in the constellation Triangulum. North is at top. This face-on spiral galaxy is just under 3 million light years from our Milky Way galaxy, and is a major member of the Local Group of galaxies of which the Milky Way is a member. M33 is about 60,000 light years across. It contains many prominent starbirth regions (pink). These are huge emission nebulae which glow as the hydrogen gas they contain is ionised by radiation from hot young stars within them. M33 is unusual in that these regions are not localised in the spiral arms, as in most galaxies.