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The Triangulum Galaxy (also known as Messier 33 or NGC 598) is a spiral galaxy about 3.14 million light-years away in the constellation Triangulum. The Triangulum Galaxy is small relative to its larger neighbors, the Milky Way Galaxy and the Andromeda Galaxy, but is about average compared to most spiral galaxies in the universe. It is the smallest of the three largest galaxies (all of them spiral galaxies) in the Local group of galaxies and may be a gravitationally bound companion of Andromeda. The Pisces Dwarf (LGS 3), one of the small Local Group member galaxies, is possibly a satellite of Triangulum.
Andreas Brunthaler reported research in 2005 that showed the proper motion of the Triangulum Galaxy, from maser-produced radio emissions, to be approaching Andromeda at 190 km/s. This was the first measurement of the proper motion of any galaxy, and amounts to tens of micro-arcseconds per year.
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General information
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The Triangulum Galaxy was probably discovered by Giovanni Batista Hodierna before 1654, who may have grouped it together with open cluster NGC 752. It was independently discovered by Charles Messier in 1764, who catalogued it as M33 on August 25. M33 was also catalogued independently by William Herschel on September 11, 1784, who assigned it the number H V.17. It was among the first "spiral Nebulae" identified as such by Lord Rosse.
Herschel also cataloged The Triangulum Galaxy's brightest and largest H II region (diffuse emission nebula containing ionized hydrogen) as H III.150 separately from the galaxy itself, which eventually obtained NGC number 604. As seen from Earth NGC 604 is located northeast of the galaxy's central core, and is one of the largest H II regions known with a diameter of nearly 1500 light years and a spectrum similar to the Orion Nebula. Herschel also noted 3 other smaller H II regions (NGC 588, 592 and 595).
This galaxy can be seen with the naked eye under exceptionally good conditions, but is often confused with the nearby and brighter NGC 752.
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See also
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