2011 01 24 Glory
Photo taken by Paul Rix, 2011 01 24
On the site Atmospheric Optics, Les Cowley describes clouds, fog and water droplets to help us understand how light plays on them to produce phenomena such as glories and sun dogs.
Clouds appear substantial and opaque because the total number of droplets is immense. Light rays are scattered after travelling just a few metres and most emerging rays will have been scattered several times. Sunlit clouds appear white because, overall, their droplets scatter the different wavelengths of visible light equally and absorb little light in the process. Colourful coronae, glories and ghostly fogbows show up when the cloud or fog has similar sized droplets and when the cloud is thin and lighting conditions are such that light rays are only scattered once.
When sunlight interacts with clouds or mist, the water droplets in the clouds are small enough to diffract and scatter its waves in all directions, creating beautiful spectrums of color such as ringed glories. Glories are opposite the Sun (anti-solar point), and can only be seen when the observer is directly between the sun and cloud that is diffracting the sunlight. In the photo above, the airplane would be in the Sun’s light path. Droplet size distribution determines how many rings the glory will have. Droplet diameter determines the size of the glory.
Looking at the photo that Paul took on the January 24th, the clouds were far enough away from the airplane that its shadow was not visible in the middle of the glory. It also looks like there is ~20% variance in water drop size distribution by looking at the lack of rings. I’m unable to estimate the size of the glory, but the angular size of the glory is only determined on the diameter the droplets (as stated above), not how far away the plane is from the clouds.
Here is another photo of a glory taken by Paul a few years ago in November 19, 2004.
Photo taken by Paul Rix, 2004 11 19
Other useful links:
Glory Formation, by Atmospheric Optics
Glory (optical phenomenon), by Wikipedia
If you’d like a little fun creating your own glory simulations, check out Les’ IRIS software.
