Moon Over Canigou

May 11, 2007

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Provided and copyright by: Alain Origné, Laboratoire Astrophysique Marseille
Summary authors & editors: Alain Origné, Jim Foster, Stu Witmer

The photo above showing a nearly full Moon rising over Mt. Canigou in the Pyrenees Mountains was taken from near Cassis, in southern France on May 11, 2006. The crimson color of the Moon is due to atmospheric absorption -- the greater path length of moonlight when the Moon is close to the horizon filters out the shorter wavelengths of light (blues, greens and yellows).

Twice a year at sunset, in early February and again in early November, the Sun on the horizon as seen from Cassis is aligned behind the 2,784 m (9,134 ft) high Mt. Canigou. The distance from Cassis to Canigou is approximately 263 km (163 mi). Normally, without considering the refraction effect of the atmosphere, this mountain is too distant to be observed; however, when atmospheric conditions are right and the Sun or Moon is perfectly aligned, Pyrenees summits higher than about 2,300 m (7,546 ft) can be detected. Eighty percent of the distance from Cassis to Canigou is over the Mediterranean Sea. When the water is colder than the air, a ray of light traveling through the lower atmosphere will be bent or refracted downward -- the image of a distant object is displaced upward (superior mirage).

Photo details: Picture taken with a Maksutov telescope, with focal length of 1,250 mm and an aperture of F/10. The digital camera was a Minolta Dynax 7D, set to 1,600 ISO, with an exposure time of 0.5 seconds. Geographical location: North 43° 12' 38" - East 005° 33' 40".

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