Also known as Messier 33, the Triangulum Galaxy is a spiral galaxy approximately 3 million light-years away in the constellation Triangulum. It is the third largest galaxy in the Local Group, a group of galaxies that also contains the Milky Way Galaxy and the Andromeda Galaxy, and it may be a gravitationally bound companion of the Andromeda Galaxy. The Pisces Dwarf, one of the small Local Group member galaxies, is possibly a satellite of Triangulum. The Triangulum Galaxy can only be seen with the naked eye under exceptionally good conditions.
The Triangulum Galaxy was discovered by Giovanni Batista Hodierna before 1654, grouping it together with open cluster NGC 752. It was independently discovered by Charles Messier in 1764, who catalogued it as M33 on August 25. Triangulum Galaxy is over 50,000 light-years in diameter, and 3 million light-years away from the Milky Way.