When the conditions are right, Scotland, Northern Ireland and parts of Northern England are the best places in the UK to see the Aurora Borealis, an optical phenomenon of the upper atmosphere. This week viewers in parts of Scotland were not only treated to a spectacular display from the Northern Lights, they also had the opportunity to see a rare moonbow.
A moonbow, as the name might suggest, is a rainbow which appears in the light of the moon. Also known as a lunar rainbow, the optical phenomenon occurs when light from the moon is refracted by water droplets in the air. They are very rare because the light emitted from the moon is much less than that of the sun. Moonbows often appear white or very faint to the human eye, however, long-exposure photographs have been successful in capturing their full spectrum of colour.
Similar to rainbows, certain conditions must be met before they appear to the observer –
- The observer must be positioned so the moon is behind them.
- The moon must be less than 42° in the sky and close to its fullest phase.
- Water droplets such as rain or fog must be in front of the observer.
The best time to see moonbows is a few hours before sunrise or after sunset.