Physics Photo of the Week

October 12, 2007

M31 - The Great Galaxy in Andromeda
M31 is the "most distant naked-eye object visible to the naked eye".  It is pretty difficult to see with the naked eye except under extremely dark and clear skies.  It is easily found with binoculars, however.  This is a telescopic photograph made with the new CCD camera and an 8-inch telescope.  Students Chloe Stuber and Jake Lyerly helped operate the telescope and camera on Wednesday, Oct. 10, 2007.  The galaxy is so huge that it takes many frames to piece together to capture the whole galaxy which is about 3 times the angular size of the Moon.  We made 11 overlapping frames that will eventually be stitched together into one large image.  The result here is only two frames.  Students will soon help assemble the total picture.

The galaxy is extremely distant, but it is the closest spiral galaxy to our own Milky Way galaxy and is believed to be very similar in structure and size as our own Milky Way galaxy.  The distance is over 2 Million light years, and the galaxy is about 100,000 light years across.  The stars number about 100 billion (1011).  The individual stars cannot be seen except in very large telescopes.  All the stars in the photograph are foreground stars in our own Milky Way galaxy.

Notice that dust lanes can be clearly seen in the photograph.  These are areas of material that will form new stars during some epoch.  Similar dust dominates the Milky Way.

M31 is featured on another Physics Photo of the Week on November 17, 2006.  Watch for more images of this when students finish assembling the complete image.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature an interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to

Click here to see the Physics Photo of the Week Archive.

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