Spiral galaxies are icons of deep space. This one is a classic. This is the Triangulum Galaxy, named for its home constellation. Amateur astronomers also know it as M33, the 33rd entry in Charles Messier’s catalog of deep sky objects compiled in the 1780s. To Messier, object #33 was another fuzzy spot he and others might confuse for comets, the objects astronomers of the day were really after.
It wasn’t until 1850 that the Earl of Rosse, observing with his monster Leviathan of Parsonstown, a 72-inch reflector telescope, managed to see M33 as something more than a nebulous glow. He saw what the photo clearly shows — spiral arms swirling around a central core. However, in those days, such “spiral nebulae” were thought to be whirlpools of gas where stars and solar systems were forming.
It wasn’t until the 1920s, with the work of Edwin Hubble, that objects like M33 were proven to be other galaxies like our Milky Way, each composed of billions of stars.
We now know the Triangulum Galaxy lies about 3 million light years away, and is about half the size of our Milky Way. That makes it the third largest member of our Local Group of galaxies, after our own Milky Way and the famous Andromeda Galaxy.
For this shot of M33, taken September 25, I stacked 6 images, each a 12-minute exposure at ISO 800 and f/6, shot with my Astro-Physics 130mm refractor and Canon 7D camera. Visible along the galaxy’s spiral arms you can see some of the reddish and cyan-coloured nebulas that are sites of active star formation in M33.
— Alan, Oct 7, 2011 / Image © 2011 Alan Dyer