(24 March 2017) Under very special conditions a bright, almost full, moon may deliver a rainbow, like this warm Summer Thursday night. This is NOT called a halo, which is a circle around the moon at greater distance (22 degrees). This lunar corona is caused by moonlight being refracted by water drops in high clouds. To get this effect, each ray of light can only hit one droplet before making it to earth. The entire corona consists of many droplets, individually scattering the moonlight. That is why it only happens with very ‘un-dense’ clouds.
The circle does include a full rainbow of colours, but that is almost impossible to observe, let alone to photograph.
This is a challenging situation. Firstly, the entire display can stop any second and normally only lasts several minutes. This one was long, around 10 minutes. Secondly one needs to set up a tripod, at a good location, mount the right lense and …. all of this before the display is over.
Only full manual operation will achieve a good outcome, because overexposure is the trick. I tried several shutter times and apertures and discovered that a short shutter time is the best option. 0.2 second, f/4.5, ISO 200. Of course the moon is overexposed, but that is the sacrifice one has to accept. I don’t like post processing, so all I did was crop it to the right size (easy with a photo taken in RAW), and reduce the whiteness of the moon itself a little bit. The colours are original.