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There are three large spiral galaxies in our Local Group of galaxies. Our Milky Way is one, of course, and we’re joined by the Andromeda Galaxy. The third large spiral galaxy is the Triangulum Galaxy (Messier 33 or NGC 598).
The Triangulum Galaxy, also known as the Pinwheel Galaxy, is located about 3 million light-years away in the constellation Triangulum. In very bright skies you can see this galaxy with the unaided eye; although, there were no historical records of it before the invention of the telescope. It was probably first discovered by Giovanni Battista Hodierna in the 17th century, but it was first identified by Charles Messier in 1764.
Astronomers have estimated that Triangulum measures about 50,000 light-years across. That’s half the diameter of the Milky Way. It has an estimated mass between 10 and 40 billion solar masses.
While most galaxies are being carried away from the Milky Way by the expansion of the Universe, Triangulum is actually drifing towards us. Well, more specifically, it’s drifting towards the Andromeda Galaxy, and Andromeda is moving towards us. It’s approaching our galaxy at a speed of 24 km/second.
We have written many articles about galaxies for Universe Today. Here’s an article about the Triangulum galaxy.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.