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Explanation: The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp composite image, a...

Bright Nebulae of M33 Credit & Copyright: Ken Crawford (Rancho Del Sol Observatory) Explanation: Gorgeous spiral galaxy M33 seems to have more than its fair share of bright emission nebulae. In fact, narrow-band and broad-band image data are combined in this beautifully detailed composite to trace the reddish emission nebulae, star forming HII regions, sprawling along loose spiral arms that wind toward the galaxy's core. Historically of great interest to astronomers, M33's giant HII regions are some of the largest known stellar nurseries - sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2003 September 24 M33: Spiral Galaxy in Triangulum Credit & Copyright: Robert Gendler Explanation: The small constellation Triangulum in the northern sky harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33's diameter spans over 50,000 light-years, making it third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2002 December 2 Nearby Spiral M33 Credit & Copyright: T. A. Rector & M. Hanna, NOAO, AURA, NSF Explanation: Spiral galaxy M33 is a mid-sized member of our Local Group of Galaxies. M33 is also called the Triangulum Galaxy for the constellation in which it resides. About four times smaller (in radius) than our Milky Way Galaxy and the Andromeda Galaxy (M31), it is much larger than the...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2002 November 2 NGC 604: Giant Stellar Nursery Credit: H. Yang (UIUC), HST, NASA Explanation: Scattered within this cavernous nebula, cataloged as NGC 604, are over 200 newly formed hot, massive, stars. At 1,500 light-years across, this expansive cloud of interstellar gas and dust is effectively a giant stellar nursery located some three million light-years distant in the spiral galaxy, M33. The newborn stars irradiate the gas with...