Last week, clouds permitting, many people witnessed a gorgeous and bright full Moon, which was the last supermoon of the year. Some luckier people also had the chance to see a much rarer event called a moonbow, which is a rainbow caused by the light of the Moon and not the Sun.
A photograph of the phenomenon was snapped by BBC Weather Watcher Andrew Hewison in the town of Alston, Cumbria, where he lives. He noticed the moonbow while walking his dog at about 22:00 UTC, and decided to immortalize the peculiar rainbow on camera.
"At first I tried to take a picture with my phone, but I couldn't make it out so I got my digital camera and put it on the night setting," Mr Hewison told BBC News.
"I was a bit rushed for time as it was only there for four or five minutes."
Hewinson added: "It's putting Alston on the map for something different."
There are several reasons why moonbows are rarer than rainbows. First and foremost, you need to have water droplets in the air opposite the Moon. The sky also needs to be dark, so it can’t be seen hours after sunset or before sunrise, and the Moon needs to be quite low in the sky – less than 42 degrees from the horizon. To top it off, the Moon needs to be at or near its brightest phase.
The light the Moon reflects on its surface is just a fraction of what we get from the Sun. Moonbows are not just rarer but also dimmer than regular rainbows. They often appear white because the light of moonbows can be so faint their colors don’t register in the color receptors in our eyes.
Long exposure photographs, like the one taken by Hewison, are a sure way to make the colors more intense. In the case of this picture, there’s also the fact that the full Moon was particularly bright as a supermoon and so slightly closer to the Earth.
Moonbows have been seen since antiquity and are not to be confused with Moon rings, another optical phenomenon where a rainbow-colored ring forms around the Moon
[H/T: BBC News]
2