M33

The Triangulum Galaxy Messier 33 (M33, NGC 598) is another prominent member of the Local Group of galaxies. This galaxy is small compared to its big apparent neighbor, the Andromeda galaxy M31, and to our Milky Way galaxy, but more of average size for spiral galaxies in the universe.  M33 may be a gravitationally bound companion of the Andromeda galaxy M31.

M33 is approaching us (our Solar System) at 182 km/s according to R. Brent Tully, or at 179 +/-3 km/s according to NED. Corrected for our motion around the Milky Way's Galactic Center, it is approaching our Galaxy at 24 km/sec.

One of the brightest and largest HII regions of M33 (diffuse emission nebula containing ionized hydrogen) has obtained an NGC number of its own: NGC 604 (William Herschel's H III.150); it is situated in the northeastern part of the galaxy, and is the bright red knot near the top of this image. This is one of the largest H II regions known at all: it has a diameter of nearly 1500 light-years, and a spectrum similar to the Orion nebula M42. Over 200 young hot massive stars (of 15 to 60 solar masses) have recently formed in this region.  Several other knots in the spiral arms of M33 have been assigned their own NGC catalog numbers as well.

The distance to M33 from our Sun is estimated to be between 2.3 and 2.9 million light-years.  With our current distance values, the distance of M33 from M31 is about 750,000 light-years. Its angular dimension of 73 arc minutes in major axis (about 2.5 times the Moon's diameter) corresponds to about 50,000 light-years in diameter, half the diameter of the Milky Way. However, the faintest outliers seem to reach farther out, so the true diameter may be at least 60,000 light-years. The mass of the Triangulum Galaxy has been estimated between 10 and 40 billion solar masses.

Image information courtesy of SEDS.

Image Details:

• Instrument: Stellarvue SV130EDT Triplet Apo Refractor OTA with Astro-Physics 27TVPH focal reducer @ f/5.4 (702mm)
• Mount: Astro-Physics AP-1200GTOCP3
• Image Scale:  2.9 arc-seconds/pixel after processing
  Camera: SBIG ST-2000XM with CFW8 Color FilterWheel
  Filters & Exposure Times:
  • L:  18 x 5 minutes binned 1 x 1  (L combined with RGB layers for L-[LRGB] Luminance layer)
  • R:  36 x 5 minutes binned 1 x 1
    G:  18 x 5 minutes binned 1 x 1
    B:   27 x 5 minutes binned 1 x 1 
  • Total equivalent unbinned exposure time of 15 hours
  Software:  Maxim DL/CCD, CCDStack, Adobe Photoshop CS2, RC Astro Gradient X-Terminator, Neat Image Pro
  Location:  C.A.A.S. East Observatory, Little Rock, AR., El. 650ft
  Date: January 2nd, 2011
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Wade Van Arsdale
Little Rock, AR., USA
January 11th, 2011