True Color of the Moon
May 16, 2011
The photo sequence above shows the full Moon on April 17, 2011 as observed from Leiden, Netherlands. The left-most photo of a carrot-colored Moon was snapped just after moonrise. Here the Moon is only seven degrees above the eastern horizon. At center, the peach-hued Moon is well clear of the horizon but still low in the sky -- 14 degrees above the horizon. The photo at right was captured two hours after the first photo when the silvery Moon was 19 degrees above the horizon.
Our atmosphere acts like a filtering lens to photons moving toward the planet's surface from space. Sunlight, moonlight and starlight are all attenuated and scattered to some degree. However, in the optical region of the spectrum, blue light is more strongly scattered than red light. This results in celestial objects seeming slightly redder than expected, especially near the horizon where, because of the greater path length of light, the reddening is much more obvious. See also yesterday's Earth Science Picture of the Day.