Three Amazing Things about Rainbows
First, most rainbows form a partial circle in the sky, which in turn suggests a full circle - and what’s at the center of that full circle? The head-scratching answer is: the shadow of that head you're scratching (or at least the spot where your head’s shadow would fall, if you could see it). Let me explain.
Every time you see a rainbow, the sun is behind you, and the sunlight bouncing off the water droplets in front of you is refracted back as the ROYGBIV colors (as if the droplets are little falling prisms). Think of your field of vision as a cone with its tip at your eyes, radiating outward from there; you perceive the rainbow along the curve of that cone. And so the center of the rainbow’s circle is the point directly opposite the sun (i.e., the point at which the shadow of your head would fall). Here’s the upshot: the sun is always behind you when you see a rainbow. Now you know where in the sky to look for one!
Second, for the same reason, every rainbow we see is the same sized arc within our visual field - whether we perceive it in a backyard sprinkler or out over some distant mountains. In other words, if you were to reach out your arms in front of you to indicate the width of the rainbow arc you see in your backyard sprinkler, your arms will be the same distance apart as they’d be if you did the same thing to show the comparable arc of the rainbow out over those mountains on the horizon. This is because the perception of the rainbow is always the result of refracted light appearing to you along the curve of the "cone" of your visual field - and the size and shape of that cone never change. Astounding - and true!
And third, have you ever seen a double rainbow (a rainbow outside another rainbow - you can glimpse one in the image above)? Well, next time you do, look closer: the outer rainbow is a reflection of the inner one, and as such, its order of colors is reversed! Not ROYGBIV, but VIBGYOR!
God’s creation is full of amazing surprises!