Physics Photo of the Week

FEBRUARY 3, 2012

First Quarter Moon
On Monday, January 30, 2012 students Allison Giles and Madeline Miller photographed the first quarter Moon through a Questar telescope using a digital camera.  Even though the Moon looks half-full, it is called the "first quarter" because the Moon is one quarter (1/4) through its orbit around the Earth in its monthly cycle.  The angle between the Sun, Earth, and Moon is 90 degrees or a quarter circle. 

At partial phase, as shown here, the craters of the Moon are highly pronounced - especially near the "terminator" or the edge of the illuminated portion.  This is due to the grazing angle of sunlight on the Moon allowing the craters and mountains to cast long shadows.  The edge of the Moon against the sky (on the right side of the photograph) is called the "limb".

When Allison took this picture, she inadvertently locked the shutter release so that the camera snapped about 10 photos in rapid succession ("paparazzi" mode).  I used this to our advantage by adding all 10 of the digital images to create a cleaner average. 

A full Moon photo is shown below in an image made last September 12 by Josh Reiss, Andrew Dutcher, and Sarah Elliott using the same equipment.  The crater shadows don't show up at all in the full Moon image, but the dark areas, called marias, are just as prominent.  The full Moon image also is noted for highly visible rays emanating from the more recent craters.  The rays consist of debris that was scattered in all directions by the catastrophic impact of a large meteor.   All of the visible craters on the Moon, even the younger ones, are at least a million years old - much older than the 400 years that people have been looking at the Moon with telescopes beginning with Galileo Galilei in 1609.

The Questar telescope used for these photos was a gift to Warren Wilson College by Ralph Brown of Chattanooga, Tennessee.

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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