What is Triangulum galaxy?
{{multiple image | align = right | direction = vertical | width = 250 | image1 = Spitzer m33.jpg | width1 = | alt1 = | caption1 = [[Infrared]] image of M33 taken with the [[Spitzer Space Telescope]]|alt=In the center is an irregular spiral ellipse of red dust and a haze of blue light from the stars. The black surroundings are dotted with individual stars. | image2 = M33.jpg | width2 = | alt2 = | caption2 = Ultraviolet image of M33 by [[GALEX]] observatory }} The '''Triangulum galaxy''' is a [[spiral galaxy]] approximately 3 million [[light year]]s (ly) from Earth in the [[constellation]] [[Triangulum]].<ref name=science307_5714>{{cite journal | author=Brunthaler, Andreas |display-authors = etal | year=2005 | title=The geometric distance and proper motion of the Triangulum Galaxy (M33) | journal=Science | volume=307 | issue=5714 | pages=1440–1443 | bibcode=2005Sci...307.1440B | doi=10.1126/science.1108342 | pmid=15746420|arxiv = astro-ph/0503058 |s2cid = 28172780 }}</ref> The Triangulum galaxy is the third-largest member of the [[Local Group]] of galaxies,<ref name=aj127>{{cite journal | author=Karachentsev I. D. |display-authors = etal | title=A catalog of neighboring galaxies | url=https://archive.org/details/sim_astronomical-journal_2004-04_127_4/page/2031 | journal=Astronomical Journal | year=2004 | volume=127 | issue=4 | pages=2031–2068 | doi=10.1086/382905 | bibcode=2004AJ....127.2031K |s2cid = 124129428 }}</ref> which includes the [[Milky Way]] galaxy, the [[Andromeda galaxy]] and about 50 other smaller galaxies. It is one of the most distant permanent objects that can be viewed with the [[naked eye]]. It is catalogued as '''[[Messier object|Messier]] 33''' or '''[[New General Catalogue|NGC]] 598''', and is sometimes informally referred to as the '''Pinwheel galaxy''', a nickname it shares with [[Messier 101]]. == Properties == === Structure === In the French astronomer [[Gérard de Vaucouleurs]]' revised Hubble Sandage (VRHS) system of [[galaxy morphological classifica