Atmospheric
Optics
Lunar Corona
By Sergio Mont�far in Argentina.
This image shows well the delicate pastel colours of a corona. The central aureole is very slightly blue grading to pale yellow and reds at its edge. the first ring starts with blues and shifts then through subdued greens to more reds.
No colours are saturated like those we see in a circumzenithal arc halo or parts of a rainbow. Instead they are mixtures. Red light coronae are larger than blue ones. A white light corona is an additive composite of the different spectral colours. Move the slider over the animation on this page.
This picture also shows nicely that we distinguish rings almost by colour alone rather than by differences in brightness.
Image ©Sergio Mont�far, shown with permission
Sergio produced the picture by manually aligning and stacking several images with different exposures.
"I opened all images as layers into one document in Photoshop, aligned the layers and then combined them using masks. There was one for details on the moon which was the shorter exposure, then the rest to reveal the other areas of the corona. The star trails that you see in the corners of the photo are from the longest exposure.
Diffraction by small droplets in cloud has likely produced the corona. Small ice crystals in high cirrus also do the same although their coronae are usually less well defined.
