All of us know very well about Rainbow but “did you ever see its cousins?” Yes rainbows do have cousins and they are Dewbows, Fogbows and Moonbows. Just as a rainbow these also are the result of refraction of light through water drops which is common to all of them. But all these are different from each other in some other aspects. Are you excited to know about them and the difference between rainbow and their cousins? Then keep reading.
Let us first talk about rainbow, rainbow is one of the most beautiful natural phenomena. When light from sun refracts through water droplets suspended in atmosphere the white light splits (dispersion) into seven colours and forms a rainbow. For a symmetrical and beautiful rainbow the water droplet suspended in air must have a diameter of some millimetres. There are many other optical phenomenon like there are
- multiple rainbows
- twinned rainbows
- supernumerary rainbows
- full circle rainbows
- monochrome rainbows
- higher order rainbows
- Circumhorizontal and circumzenithal arcs
let us know about the three cousins fog bow, dewbow and moonbow as of now and we will talk about other phenomenon in later articles.
Fogbows are formed when sunlight refracts through fog. The water droplets which form fog are very small in size with a diameter of only 0.05 millimetre. Fogbows are white in colour and thus they are also known as white rainbow.
According to NASA:
The fogbow’s lack of colours is caused by the smaller water drops … so small that the wavelength of light becomes important. Diffraction smears out colours that would be created by larger rainbow water drops.
If fog have larger droplets then we can see pale colours in it.
Rainbows and fogbows are formed in sky but Dewbows generally are seen on grass, on spider web and on leaves where dew forms.
Sun light when refracts through dewdrops formed we can encounter a Dewbow.
Dew bows are generally formed in outdoors early in the morning after a clear night and that too when temperature is below dew point.
Generally rainbow is a circle but Dewbow has a shape of hyperbola. Theoretically if it forms when sun is high in the sky, it can take a shape of ellipse or parabola but practically it is not possible as dew evaporates by the time sun comes above it.
Elliptical Dewbows can be seen rarely when full moon high in the sky illuminates fields with dew drops.
The major difference between rainbow and moon bow is that moon bow is formed due to moon light and rainbow is due to sun light.
Moonbow is formed when light from moon refracts through water droplets. This is generally observed during full moon days.
Moonbows have pale colours due to insufficient light. For it to form the sky must be very dark, there must be rain opposite to moon or there must be a waterfall, the sky must be clear and it should be a full moon day. All these make a Moonbow rare but still we see it now and then.
So that sit for this article
Did you ever see a halo? Do you know about it? Want to know about it, then keep reading our articles and you will soon get an article about other beautiful natural phenomena.
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