SAN ANTONIO — How does a rainbow form?
To start, you need two main ingredients: The sun and the rain. As the incoming light moves through rain, each individual water droplet acts as its own glass prism—reflecting and refracting the light so that it appears in different colors.
And why do we see these different colors? We learned about this in science class...say it with us: ROY-G-BIV. That stands for red, orange, yellow, green, blue, indigo and violet; essentially, the different colors on the spectrum.
But why do we see the colors arranged where red is at the top and blue is at the bottom? Well, the red is on top because the light travels a longer distance to us, hence you need the longer wavelengths associated with the color. Blue is on the bottom because light has the shortest distance to travel from us, hence the shorter wavelengths of blue and violet are visible.
Putting it all together, the sun forms on the opposite sky from the sun. It must be within a couple of hours of either sunrise or sunset, you must be between the rain and the sun (with your back at the sun) as it forms in a full arc at an angle of 40 to 42 degrees.
Finally, the person next to you sees it differently from their vantage point.