White Moon and Pink Contrail
May 02, 2007
On the walk from my car to work on the morning of January 11, 2007, the contrast between the bright white Moon (at first quarter phase) and the pink contrail that had blown past it caught my eye. I snapped the photo above, and turned it into a lesson for my earth science classes that morning. With the photo on the screen, I asked my students to explain how, while both the Moon and the cloud were illuminated by the same Sun, the cloud was pink and the Moon was so white.
The answer lies in the fact that the atmosphere absorbs and scatters the shorter (blue) wavelengths of light, while allowing the longer (red) wavelengths through. The low angle morning sunlight arriving at the cloud (contrail) had traveled through significantly more atmosphere than the more "pure" sunlight reflected by the Moon. Photo taken near Bedford, New York.