M74, (NGC 628) a spiral galaxy. Image above has been cropped and downsized for display. Click on image for full frame full resolution picture with its neighbor M65. |
M74 is among the first of 14 "Spiral Nebulae"
discovered before 1850. It wasn't until the late 1920's that it was realized
that these were not nebula, but galaxies at great distances beyond our own.
It is of classical face on spiral appearance. Its distance may be
about 30 to 40 million light years, which would make it about 95,000 light
years across, or about the same size as our
Milky
Way galaxy. The arms are maybe 1000 light
years wide, which spiral out to cover a region more than 10 arc
minutes of diameter, and include clusters of blue young stars and pinkish
colored diffuse gaseous nebulae. These glowing knots or clusters also shine
in the UV, and altogether indicate very active star forming regions. The remarkably symmetric appearance over the whole galaxy is probably caused by the phenomenon of density waves sweeping around M74's gaseous disk, probably induced by gravitational interaction with neighboring galaxies. When gas clouds orbiting within the disk encounter such density waves, they are accelerated into the spiral shaped wave crest, and then slowed down, so that they converge toward the spiral arm, enhancing the effect of the density wave. Moreover, collisions and mergers of neighboring clouds occur, which are thought to induce the knots of star birth activity along the spiral arms. M74 can be found in the autumn sky about 15 degrees above the celestial equator, below and to the east of Andromeda (M31) almost 15 degrees directly below M33. It can be difficult to see much of M74 under the slightest light pollution or other imperfect viewing conditions, as its nucleus is almost stellar, and the disk and spiral arms of considerable low surface brightness. A telescope of 10" and larger is generally needed to see detail. The longer exposures of astrophotography can nicely show it's true form. |
10"
F6.3 Schmidt Cassegrain Telescope, (1600mm F.L.) Modified Canon
300D camera with IR-UV filter, placed at the scopes prime focus |