On July 31, 2015 was a “blue moon” (second full moon in a month). The weather forecast for that night in Spain was storms and heavy rains. I was travelling from Madrid airport to the north of Spain. The first atmospheric phenomenon was a 22 degree halo that I photographed in the rural areas of Castilla. Then the storms began and the blue moon disappeared. At 5am I was already at my home in Villaverde, Leon. It was raining all night but then only for a few minutes the moon appeared again on the wester horizon and produced this double moonbow with Alexander’s dark band.
I created also a short timelapse video of a second moonbow , late that night, just before dawn. Pictures taken with Nikon D5300, Nikkor fisheye 10,5 mm, f:2,8, ISO 400, 20 sec exposure.
Author: Roberto Porto, Spain
Colourful coronae around the sun and the moon are caused by light diffraction at water droplets in medium level clouds. Normally these coronae are circular like this case, as they indicate that the droplets in a cloud are all of about the same size. If only a 10% of the droplets vary in size, the corona already appears blurred. (see left figure)
In this observation, made by Bertram Radelow at Davos, Switzerland, in the evening of October 10, 2011 at moonrise, the corona showed very brilliant colours but nevertheless was rather “egg-shaped”. Bertram Radelow said the corona appeared in very thin clouds which could not be seen with the naked eye. Probably there were thin orographic clouds (as can be seen here). In these clouds, droplets are often largest in the centre of the cloud and getting smaller gradually towards the rim, so that the colours are preserved because in a given plane the droplets are still of about the same size.
In this example it looks as if two layers of clouds with different sized droplets are positioned above each other, causing a kind of break in the gradient of the corona.
This photo was taken by Claudia Hinz at the evening of Jan. 11th, 19.35 CET from Mt. Wendelstein (1838m), Southern Germany. The full Moon in this night was extra bright. Dr. Elmar Schmidt of the SRH University of Applied Sciences in Heidelberg, Germany, used an absolutely-calibrated photometer to precisely measure the moonlight and found it more than 50% brighter than that of a typical full Moon.
1. The Moon was at perigee, the side of the Moon’s elliptical orbit closest to Earth.
2. The Earth-Moon system was near perihelion, the side of Earth’s elliptical orbit closest to the sun. Extra sunlight increased the reflected luminosity of the Moon.
3. The Sun-Earth-Moon trio were almost perfectly aligned. This triggered a strong opposition effect an intense brightening of the lunar surface caused by the temporary elimination of normal shadows.
4. The weather conditions were optimal for photometry due to the clean and dry arctic air (its relative humidity being less than 10% at the moment of the photo). This resulted in only clear air scattering of moonlight with no extraneous glare as evident in the completely blue night sky. The brightness of the mountain landscape was additionally increased because of the reflection from the snow.
Elmar Schmidt details the relative contributions of each factor in his full report.
Authors: Elmar Schmidt & Claudia Hinz
Well, I wanted to observe moon halos that evening, but the sky was totally clear without any cirrus clouds.
I noticed that some blades of the plants on a field were rather wet. I walked some steps into the field and immediately noticed a clear brightening around the shadow of my head. I did a few steps to the left and to the right and could see a very faint dew bow. So I took some photographs at different exposure times and ISOs. The best photographs (1 2) I achieved using stop 4, an 18-mm-lens and at a time of exposure of 45 seconds at ISO 400.
Author: Michael Großmann, Kämpfelbach, Germany
In the evening of February 14, 2008, an orographic cloud similar to this one formed above a sea of clouds under the influence of foehn wind above Mt.Wendelstein (1838m) in the Bavarian Alps. In this orographic cloud, an corona appeared around the moon which was more intensive and larger than any corona I had seen before. 4 systems of rings were clearly visible. The intensitiy leads me to the conclusion that all water droplets in the cloud were of the same size.
As I had a position very close to the cloud, the corona was extraordinarily large. A comparision to the constellation of Orion shows that it had a diameter of more than 20°. Below its lower part, the corona turned into a faint pink and green iridescence, indicating that the droplets were smaller towards the rim of the cloud. And it was also interesting that the thin cloud as well as the corona did not show greater changes in intensity and shape for about 4 hours. They only dissolved when the foehn wind broke down and the clouds of a masked upper level cold front came up.
Author: Claudia Hinz, Brannenburg, Germany