Blue Earth, Blue Moon

December 31, 2009


Photograph: from the crew of the International Space Station; Gateway to Astronaut Photography of Earth
Summary Author: Jim Foster

The photo above showing a somewhat oblate and partially tinted Moon was captured from the International Space Station (ISS) on May 11, 2009, over the Pacific Ocean. The watery blue color as well as our lone satellite’s rather flattened shape is attributable to the Earth’s translucent atmosphere. It refracts and scatters moonlight (sunlight and starlight too). From space, the lunar disk is virtually colorless; they’re no pumpkin, jonquil or oatmeal colors that we can see from Terra firma as the Moon traverses the sky. However, aboard low orbiting spacecraft, if the Moon happens to be “rising” above the Earth (or “setting” behind it); it attains a blue hue when observed through the layers of our atmosphere.

Tonight is the second full Moon of the month and therefore earns the moniker “blue Moon” based on the more modern definition, which simply requires two full moons to occur in a given month. The original definition, according to Maine Farmer's Almanac, is a bit harder to achieve -- the "blue Moon" is referred to as the third full moon in a season having four full Moons. Since tonight’s full Moon is the first of the winter season, it doesn’t meet the original’s stipulation to qualify as a “true” blue Moon. Blue Moons (two moons in a calendar month) are observed on average about once every 30 months -- the next one occurs on August 31, 2012. However, based on the old standard, there will be a blue Moon in November 2010. The next blue Moon to fall on New Year's Eve will occur in 2028.

ISS Tracking Page