Facts about Rainbows
- You need sun and rain to form a rainbow, but it doesn’t have to be raining where you are. The rain could be overhead or a mile or more away.
- Not surprisingly rainbows are rare in the desert. Luckily I live in Lancashire and we get lots of rain showers. I see rainbows about twice a month on average and I bet I’d see more if I wasn’t stuck inside at work most of the week!
- When the sun is low in the sky you get a taller rainbow. Therefore sunrise and sunset produce the tallest rainbows.
- Big raindrops produce the brightest rainbows. Hurray for heavy rain showers!
- Although we usually see them as semi circles or less, rainbows have the potential to be complete circles. Normally the lower half of the circle is below the horizon, but if you are in a plane or the sun is low and you are in the mountains you might see more of the circle.
Richard Of York Gave Battle In Vain is a commonly used mnemonic for remembering the order of the colours in a primary rainbow. Going from from the outside to the inside - Red Orange Yellow Green Blue Indigo Violet. In a secondary rainbow the order is reversed.
However, because the colours actually mingle at the edges we actually see a much wider range of colours and shades in a rainbow.
It is impossible to reach the end of a rainbow, because the rainbow moves away as you go towards it. But seeing the end of this particular rainbow so clearly I could understand that people might go mad feeling that they could reach the actual end of it, but never quite managing to.
In Irish myth leprechauns, who are capricious creatures, are said to hide their pots of gold at the end of rainbows.
The reddest rainbows occur at sunset and sunrise. This is because when the sun is very low in the sky the rays have further to travel through the lower atmosphere and get increasingly dispersed by dust and particles. The green and blue light waves get more dispersed than the red ones hence rainbows which look mostly red.
The main rainbow is known as the primary rainbow, but outside it a fainter secondary rainbow is often visible. Together they are often described as a double rainbow. Because of the way light refracts through water droplets in a primary rainbow the red is on the outside of the bow, in a secondary rainbow the light is on the inside of a bow.
The dark sky between the two rainbows is called Alexander’s Dark Band. It’s named after the ancient Greek philosopher Alexander of Aphrodisias, because he was the first person we know of to have described it in writing.
A bit like conjoined twins this is where a rainbow appears to split part way along and then rejoin. It is a very rare phenomenon.
Iridescent Cloud and other Rainbow-like Effects
There are some other phenomena which produce rainbow colours in the sky which aren’t rainbows, but are just as beautiful. Irridescent clouds are a rainbow effect in cloud usually quite near the sun. They are caused by the sunlight hitting water droplets at the right angle. There are a group of rainbow type effects called ice halos such as the parhelia and circumzenithal arc. You do need to take care when looking out for these things and shield your eyes from the sun. If you are taking photos with an SLR camera do not look through the view finder.
Sundogs, also known as parhelia, appear on sunny and even hot days with no rain in sight. They occur when sun rays hit ice crystals in cirrus cloud near the sun. The sundogs are about the same level in the sky as the sun, but the lower the sun is the nearer the sundogs will be to the sun. There is usually one on either side of the sun, but depending on the cloud you may only see one on one side.
They might have been named because they appear to follow the sun a bit like dogs. Alternatively, because appearing on either side of the fiery sun they reminded people of firedogs which are supports for a fire grate often made of wrought iron or brass.
Sun dogs are relatively common throughout the world, but tend to last for quite a short time and often go unnoticed. In the first eight months of 2012 I have seen sundogs in Lancashire on four occasions.
Upside Down Rainbows
Upside down rainbows are rare but they do occur. Sometimes called sun smiles they are officially known as circumzenital arcs. Like sun dogs they occur due to light refracting off ice crystals in wispy cirrus cloud above the sun. I haven’t seen one, but really hope to one day. A circumhorizon arc is a similar effect, but with a shallower curve seen in cirrus cloud below the sun when the sun is high in the sky. Because the sun needs to be high it is quite common in much of America, but rare in the UK. I shall have to be especially lucky to see one in Lancashire since we get a lot of rainy days.
Since rainbows are a natural phenomenon which will have been seen by the earliest humans, it is not surprising that they feature in the mythology and religions of many cultures.
In Greek myths, Iris, the daughter of an ocean nymph is the personification of the rainbow.
In the Christian bible, after the great flood, it is claimed that God made the rainbow as a sign that he would never destroy Earth by flood again.
In Norse mythology there is a rainbow bridge between where the realms where the Gods and humans live. Perhaps this was the inspiration for the 'Rainbow Bridge' poem habit in today's culture of saying that beloved pets pass on to Rainbow Bridge.
Many poets have written about rainbows. One of my favourite rainbow poems is 'Birth of Rainbow" where he describes seeing a cow licking her newborn calf whilst she's stood under the end of a rainbow. By chance I recently came across such a scene myself which added an extra element of wonder to the recent birth.