Physics Photo of the Week

November 15, 2013

Messier 31 - The Great Galaxy in Andromeda
The Solar System's closest external spiral galaxy is the Great Galaxy in Andromeda - also called Messier 31 after the 18th century astronomer Charles Messier who cataloged about 100 nebulous objects in the sky to distinguish permanent objects from transient comets.  Edwin Hubble studied this galaxy extensively in the early 20th century using the largest telescope at the time (the 100 inch reflector at Mt. Wilson, Calif).  Hubble discovered that this galaxy was an amazing 2 Million light years distant, and consisted of over 100 billion (1 x 1011 stars).  Click on the image for a larger view.

This galaxy is in prime viewing position (high overhead) on November nights, and can be easily seen with binoculars.  A sky map and early image with more primitive equipment was displayed on PPOW for November 17, 2006.  A higher resolution telescopic image is shown on Oct. 12, 2007

This week's photo was taken using a CCD camera, but with a short focal length lens (135 mm) taken without a telescope.  The camera and lens were "piggy-back" mounted on the 14 inch telescope at College View Observatory.  The galaxy from 2 million light years away (Earth's view) is so large (about 3 full Moon diameters) that a big telescope has to make a mosaic of many pictures to include the whole object.  The small lens on the CCD camera can obtain the full extent of the galaxy in one shot at the expense of resolution.  All the stars in the photograph are foreground stars in our own Milky Way galaxy (a twin to M31).  A higher resolution photo of the galaxy is being planned, but will take awhile due to the many images needed.

Two other satellite galaxies are also displayed here and labeled in the negative image at right.  These are ellipsoidal galaxies, M110 and M32, which are in slow orbits around the large spiral M31.  M32 is almost spherical and looks very much like one of the brighter stars.  With greater resolution through a larger telescope, the stars will be rendered more point-like, but M32 will still exhibit a spherical appearance.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature 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

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

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