Onlinity Learning

Let's remember some foreknowledge, first. We all know that for the formation of a rainbow sun and rain are needed, and that it will not form in the absence of either of them. So, formation has something to do with the light passing through water.
Because water is denser then air, light passing through raindrop slows down and changes direction, exiting at different angle. This is called refraction. Sunlight (which appears white to us) is made of different colors, each with its own wavelength, and slowing by different amounts. This leads to dispersion - process of separating white light to all colors of visible spectrum (red, orange, yellow, green, blue, indigo, and violet).

After this happens, when standing in the right place, an observer may see refracted and dispersed light, forming the rainbow. Arc's center stands in the antisolar point - point directly oppsite the sun. Different colours exit the droplets at angles that vary by around two degrees from red (with the longest wavelength, around 650 nanometers) to violet (with the shortest wavelength, around 400 nanometers), so red will be the first, and violet the last color on the rainbow. Ultrared and ultraviolet light can also be found in it, but human eye cannot register these wavelengths.

Interesting things to notice:

If an observer is att high enough altitude, his antisolar point is also raised from the ground. That leads to the rainbow forming as a full circle!
As no two humans can stand in the same place, they can not have the same antisolar point, so their rainbows are in different places. This means that if you see the rainbow, no one else can see the same one, it is only yours!

Key words:

refraction - changing light's direction and speed when ambience density changes
reflection - light bouncing of a surface
dispersion - separating colors that make up white light
antisolar point - point directly oposite to the sun

How and why do rainbows form?