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.
2012 December 20
Explanation: The small, northern constellation Triangulum harbours 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 25 panel mosaic, nicely shows off M33's blue star clusters and pinkish star forming regions that trace the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 1 o'clock position from the galaxy centre. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U.