Physics Photo of the Week

October 20, 2006

Student Photographs of Full Moon

On October 5, 2006 (about 2 weeks ago) the astronomy students at Warren Wilson College photographed the nearly full Moon through a telescope.  The actual full Moon occured at about 11:00 PM on Oct. 6, 2006, a little over one day after these photos were taken.

The techniques for photographing the full Moon involves a special eyepiece fitted to an 8-inch telescope to which a digital camera is attached.  The special eyepiece is a tremendous help because it holds the camera firmly in position.  We used to do these photos merely by handholding the digital camera close to the eyepiece.  Another important technique is to use a time-delay shutter release.  The time-delay allows the vibrations of the telescope caused by pressing the shutter release to die-out.  This allows an un-smeared photograph. 

Photographs of the full Moon show the darker areas - called maria - in contrast to the lighter areas - called highlands.  The dark maria (Latin for "seas") were caused by catastrophic events early in the Moon's history.  It is believed that these catastrophic events were collisions of the Moon with minor planets or large asteroids.  The giant craters ruptured the outer crust of the Moon allowing the denser material from inside the primordial Moon to rise to the surface.  This darker material then solidified into the relatively flat areas called the maria.  Because the maria material is more dense than the rest of the lunar surface, and because the maria are predominantly on one side of the Moon, the side of the Moon with the maria is "tidally locked" in the orbit around the Earth.  This is the main reason that the same side of the Moon faces the Earth at all times. 

There are a few relatively "recent" impacts on the Moon.  These are seen as craters with the rays of lighter material readiating out from them.  The most obvious is Tycho in the lower left with the extensive ray system.  Copernicus and Kepler are also prominent "recent" impact craters in maria in the mid-upper-left parts of the image.

Further study of this image, and a closeup image shown at right, reveals that the Moon was not quite full on Oct. 5.   Dan Callaghan chose to zoom in on the upper left part of the Moon.  Notice that the topographic features of the craters are visible in Dan's photo near the edge of the Moon.  These features are visible because the Moon was not quite full.  These craters lie at the "terminator" - the boundary between the sunlit part of the Moon and the dark part of the Moon.  At the terminator, the sun is low to the lunar horizon and shadows are long and enhanced.  A partial phase Moon shows the topographical features much more prominently.  This occurs when the terminator falls on the middle part of the Moon that faces Earth as in the PPOW for September 9, 2005.

The full Moon for these photographs occured about two weeks ago.  If you look for the Moon tonight (October 20, 2006) you will not find it because the Moon is "new" - between the Sun and the Earth.  In two weeks (November 3, 2006), when the next Physics Photo of the Week will be published, the Moon will again be full.   Due to fall break, there will be no Physics Photo of the Week next week. 

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