Physics Photo of the Week

Warren Wilson College

November 19, 2004


Cassiopeia is a very prominent constellation in the high northern skies these nights.  Will Rutherford, a student in Contemporary Astronomy at Warren Wilson College photographed the constellation with a digital camera by taking many 15 second exposures while the camera was mounted "piggy-back" on a telescope equipped with a clock drive, so that the constellation was in the same place in the camera field of view as the earth rotated during the 10 minutes of picture taking. The camera was looking directly at the sky, not through the telescope.  The frames were further aligned and digitally added by Physics Assistant Dan Sockwell.  The "co-adding" increases the visibility of faint stars.  Notice how many faint stars are visible using this technique.  Cassiopeia is also in the Milky Way - a part of the sky which is quite rich in numbers of stars.

The asterism of Cassiopeia is the familiar "W" formation made by the bright stars as shown in the image at left.  The color and contrast of the stars in these images have been enhanced to exaggerate the various colors.  Notice that most of the bright stars are quite blue - indicating that they are extremly hot - about 4 times hotter than the sun.   On the other hand, the bright star in the lowest part of the "W" is yellowish, indicating it is about 2/3 the temperature of the sun.  Look for Cassiopeia next time the stars are visible!   More information about the stars in Cassiopeia may be found at the SEDS web site:

The Contemporary Astronomy class at Warren Wilson College will soon analyze the relative brightness of the stars in this photo by means of a computer photometry program.  These students will calculate the stellar magnitudes and the intrinsic magnitudes: the brightness of all the stars if they were placed at the same distance.

Due to Thanksgiving break, there will be no Physics Photo of the Week on November 26, 2004.  The next photo will be published on Dec. 3.

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 all Physics Photo of the Week for 2004.