Are Rainbows Actually Circles?

Rainbows: they’re like the unicorns of the sky—beautiful, mesmerizing, and often the subject of myth and wonder. But have you ever paused and wondered why rainbows are curved? Or even more intriguing, are they just partial arcs or full-on circles?

The Geometry Behind Rainbows

Rainbows are the result of a rather intricate dance between sunlight and raindrops.

When sunlight enters a raindrop, it bends, spreads into its various spectral components, reflects off the interior of the raindrop, and finally exits, scattering into a spectrum of colors. The technical term for this phenomenon is dispersion.

Now, here’s where geometry comes into play. The light’s angle as it exits the raindrop varies for each color, usually between 40 and 42 degrees for primary rainbows.

As a result, what we typically see is a circle with a radius of around 42 degrees from the antisolar point (the point directly opposite the sun).

Full Circles? You Bet!

Most people are familiar with the semi-circular rainbows arching across the sky. But did you know that rainbows are actually full circles? That’s right; most of us just see the top half because the ground obstructs the bottom part.

If you’re ever lucky enough to view a rainbow from an elevated vantage point with a clear sky and raindrops below, you might catch this phenomenon in all its 360-degree glory.

Optical Illusions and Limitations

Here’s a reality check: even though the physics says it’s a circle, the visibility of a rainbow depends on various factors.

Light intensity, droplet size, and observer location all affect how much of that colorful circle you’ll see. And let’s not forget the atmospheric conditions; they need to be just right.

Wrapping Up

So, are rainbows circles? In short, yes. They’re full circles, but the ground and other conditions usually keep us from enjoying the complete geometric marvel.

The next time you see a rainbow, you’ll know you’re catching a glimpse of something even more extraordinary than it appears at first sight.