Monday 17th to Sunday 23rd February 2025
The Engagement Ranger at Ham Hill, where I run some of my astronomy talks, asked me a question the other day and it prompted me for an interesting topic here. She had seen a white ring around an almost-full Moon - a phenomenon known as a "Moonbow".
This is a rare occurrence where sunlight reflected from the lunar surface is refracted by water droplets as it passes through our atmosphere. If the light is quite strong, you may even see the colours of the rainbow, just like a regular rainbow here on the Earth, although the Earth-based ones are much more obvious as the sunlight is coming direct from the Sun and so is far more intense.
White light, that originates from the Sun, is a combination of the three primary colours - red, green and blue. If white light reflects off a surface (like a mirror) it stays as white light. If white light passes through a lens or prism (or in this case, water droplets), then the different wavelengths of light or colours take slightly different paths and it has the effect of splitting up the colours - this is refraction.
The sky is blue during the day because white light coming from the Sun is scattered by tiny air molecules. Blue light has a shorter wavelength than red, so the blue light is scattered more - hence the sky looks blue. When the Sun is low in the sky at sunrise and sunset, its light has to travel further through our atmosphere and then the blue light gets scattered so much that the red light, which has a longer wavelength, can then pass through and be detected by your eyes.
Having mentioned Ham Hill at the start.....a reminder that my next astronomy talk and star party at their Visitor Centre is scheduled for the evening of Friday 28th February. Please contact the Rangers Office on 07973 887129 to reserve a place.
www.starsoversomerset.com
Screenshots courtesy of Stellarium
Moonbow image courtesy of
Copyright Adrian Dening and Radio Ninesprings 2025
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