December 23, 2004

Double Rings

Image Credit: Dominique Dierick, aka Dodi

Double Rings When I see a halo around the Moon I feel lucky at witnessing such a magical sight. And I usually explain to someone that its due to sunlight, bounced off the Moon and refracted thru ice crystals in the atmosphere to our eyes. But this wonderful picture is not of a halo, nor even two halos. A halo is a ring 44 degrees wide, but these rings are much smaller - the inner one is 2.5 degrees in diameter, and the outer is 5 degrees. Such small circles are called coronas, and the small size results from the light being diffracted by water droplets or small needles of ice. The color sequence from the inside out is blue, yellow, red. Multiple coronas occur when water drops of different size are present. The next time thin clouds obstruct your view of the lunar surface check to see if there is, no not a silver lining, but diffraction ring or corona. And also pay attention when thin clouds cloak Venus, Jupiter and Sirius, for small and faint coronas have been occasionally seen around them! — Chuck Wood Technical Details: Nikon 180mm and Nikon D70 Related Links: Dodi's Twilight Zone of Photography Corona Yesterday's LPOD: Swell Linne Tomorrow's LPOD: Introducing PlanetWarp! VOTE FOR YOUR FAVORITE LPODs! During Dec 25 thru Dec 31 LPOD will feature LPODs from the past year that visitors like best. Send me an email with your favorite seven LPODs - include their titles and the dates they appeared. Thanks!

Author & Editor: Charles A. Wood

 

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