October 02, 2011
Late summer and early fall in the Northern Hemisphere is a great time to observe the Andromeda Galaxy (M31). Fortunately, from my viewing location in Austria (Bruck an der Glocknerstraße), at the end of August (2011) there were several clear, moonless nights with near perfect transparency. M31 was stunning! As shown above, the blue regions are stars that are hot and young. The red regions are hydrogen-alpha (H II) -- this is where the blue stars are born. Observations of M31 by the Spitzer Space Telescope in 2006 revealed that our neighboring galaxy contains approximately one trillion stars. This is at least 2 1/2 times the number of stars in our own galaxy -- estimated to be between 200–400 billion.
Image details: Skywatcher Black Diamond ED80 (510 mm); imaged on 8 different nights in late August (2011); total exposure time of 34 hours (Ha = 8 hours, L = 14 hours, RGB = 12 hours). Skywatcher was unable to capture M31 in a single frame.