Interseting facts about RAINBOW you might have missed!

We remember rainbows as studied during school day, that it occurs due to reflection, refraction and dispersion of sun rays from the water droplets. Though we thought that it's a very complicated thing but actually its just a tip of the iceberg. Actually rainbow (usually we associate it with visibility of spectrum in sky during rain), is name of one of several phenomenon which gives us optical illusion. 

But for most of us, including me, after school days rainbow has merely become an social media update thing. 

Today at Pune weather was very pleasant and it marked the beginning of monsoon. Today it was one of those lucky day when I saw double rainbow. I was relieved from the heat and delighted to see rainbow and decided to capture few pictures.

Beautiful rainbow captured at Baner, Pune.

Lot of interesting and curious events happened today while capturing photo's and I decided to dig further. I will try to stick to interesting fact related to rainbow and my experience, but may include more if something is really intriguing.

Shape and Location of Rainbow

As an average observer we always see semi-circular rainbow and its located on opposite side of sun. But rainbow is not always semi-circular. Because we view the rainbow from the surface of ground and the centre of the rainbow circle is at the line intersecting from sun to rainbow circle via water drop which is causing dispersion. Thus largest rainbow we usually see is from surface of earth at diametrically opposite side of sun is at most 50%, and as you might have correctly guessed, largest rainbow can be viewed only at sunrise and sunset.

Extrapolating it further, so it must be somehow possible to see full rainbow circle. For that to happen, we must be at higher location then surface of earth and water droplet. This combination can surely give you optical illusion of full circular rainbow and it will be visible towards the surface. I remember seeing circular rainbow around sun, i.e. sun and rainbow in same direction. But those are categories as glory and halo's. Halo's are not limited to Sun, I have also observed halo's around moon.

Circular rainbow, image found in public domain. 

Color of Rainbow

We all know that we can see seven color in rainbow, i.e. if we observe closely an human eye can distinguish seven different colors. But do you know in what order these color appears? If you have studied in India, you might have remembered VIBGYOR.

In primary rainbow, one which is usually brightest in case multi-rainbow (yes, there can be multiple rainbows), have red color on the outer most ring and violet on inner side. While in case of double rainbow, which appears at 10° outer side from primary rainbow, has color visibility order opposite to primary rainbow. You can observe that in below image.

Double rainbow, captured at Baner Pune on 9th June, 2015. Notice the order of colors in primary and secondary rainbow are opposite.

You might have also missed to notice that inner side of primary rainbow is brighter then outer side. This is because all the lights dispersion from water droplets are scattered on the entire inner circle of primary rainbow and not just at the circumference. Alistair Fraser, coauthor of The Rainbow Bridge: Rainbows in Art, Myth, and Science, explains: 

"Each color has a slightly different-sized disc and since they overlap except for the edge, the overlapping colors give white, which brightens the sky on the inside of the circle. On the edge, however, the different-sized colored discs don't overlap and display their respective colors—a rainbow arc."

Light is diverted from other part of primary rainbow towards inside, making outer side appear darker.

Double rainbow

The most spectacular rainbow displays happen when half the sky is still dark with raining clouds and the observer is at a spot with clear sky in the direction of the sun. The result is a luminous rainbow that contrasts with the darkened background. During such good visibility conditions, the larger but fainter secondary rainbow is often visible. It appears about 10° outside of the primary rainbow, with inverse order of colors. Secondary rainbow, too, is visible in above image.

Bridge of Rainbow

If you are keenly reading, then you must have concluded that outer side of primacy rainbow is darker then inside. But in case of double rainbow, because secondary rainbow is in reverse direction, the inner circle of secondary rainbow must become even more darker. Hence this makes layer between primacy and secondary rainbow the darkest. As you can see in the pictures below, it looks like a bridge and hence I guess, its called Bridge of Rainbow.

Bridge of rainbow to heaven... 

Top view of rainbow bridge connecting white building on left to my upstairs neighbors balcony.

Photography of Rainbow

It was such a beautiful double rainbow and it was almost sunset, hence semi-circular rainbow was visible. I captured few images, but soon enough I realize that from that particular location I was not able to capture entire rainbow in single shot, I tried changing my location, but it did not helped. Finally, I decided to move away (go backwards) from rainbow, change building rooftops to capture the entire semi-circular rainbow. Even after moving back, I faced the same problem. Soon I got busy capturing the beauty as much I can and capture below photo.

Almost semi-circular double rainbow, 64° :)

Later, when I was going through photos on my desk, I remember the problem of not able to capture entire rainbow. Turned out that it is difficult to photograph the complete semicircle of a rainbow in one frame, as this would require an angle of view of 84°. This is because of two reasons

1. The angle of dispersion at which we see rainbow is 42°. Apply this on both the sides.
2. Rainbow is optical illusion with respect to where you are standing and not from particular location.

I had a 35mm focal length wide angle camera which spans 64° angle of view. Hence no matter what I do, I won't be able to capture 20° of rainbow. Also, when you see the end of rainbow touching the earth surface, you feel like that's the origin, but that's again, just an illusion. 

Rainbow originating from the godly tree

A person standing near that tree will see rainbow far distance at 42° in both the side. In such difficult photo capturing situations, photo stitching softwares like Google's photosphere and panoramic view comes to rescue. I took the below photo via Nexus 4, photosphere feature.

Photosphere capturing entire semi-circular image. Original image can be found here.

Other interesting facts

These are just few of the interesting things I found while reading and capturing photo, spent like 2-3 hours. I would also like to add few more intriguing one liners about rainbows and where other then this situation we can find rainbow like things?

1. Rainbow's can be created via moon light too, called Moonbow.
2. The rainbow effect is also commonly seen near waterfalls or fountains. Next time you see a fountain and clear sky don't forget to observe rainbow. 
• (Updated) Check the below photo for rainbow effect at waterfalls, also notice second lighter rainbow on right side and colors orientation.
3. It is believed that Titan, moon on planet Saturn, too have rainbows because of its moist atmosphere. But it will be difficult for me to capture rainbow on Titan, because Titan's angle of dispersion is 49°.
4. There are different type of rainbows like Supernumerary view, Reflected & Reflection rainbows, monochrome rainbows (single color), Fogbow, 22° Halo, Glory etc.

Rainbow effect at Athabasca Falls, Jasper National Park, Canada. Photo courtesy of my friend Devshree Sane, original here. 

One personal experience

While sorting and editing photos in aftermath, at one point of time, I suddenly started feeling that I am so lucky, because I had witnessed this double rainbow. Though, I strongly oppose such ideas, but the feeling was so overwhelming that I could not help but to feel happy about it. I hope this feeling stay for sometime.

That's it on rainbow's for now. I hope you too felt it as fascinating as I did. Please let me know what do you feel about the post, correct me if there were any mistakes or I missed something important which you think I should include or any type of feedback is also equally welcome.