What Leads to the Formation of a Rainbow When There’s No Rain?

When the sun emerges after a rain shower, the sight of a rainbow is no surprise—it’s a typical rainbow scenario. What’s occurring is that sunlight first bends and slows down (a process known as refraction) as it enters raindrops; it then reflects off the opposite sides of the droplets, exiting the way it came in, refracting again as it transitions from water to air. This variation in the angle of refraction creates a band of separate colors.

With that in mind, a rainbow without rain seems unlikely. So how can it occur?

According to meteorologist Rachael Witter from New York, as she mentioned on 96.1 The Eagle, it’s possible that the rainbow you see was formed by rain—but the rain evaporated before it reached the ground. This phenomenon, known as virga, sometimes appears as a faint streak hanging beneath a cloud.

Rain isn't the only type of water that can create a colorful streak or arc in the sky. A variety of phenomena occur when light bends and reflects off ice crystals in the atmosphere. Some of these halo phenomena don’t display rainbow hues—like the beam of light, called a luminous pillar, that often rises above the sun at dawn. But others do show colors, and their classification depends mainly on angles and the sun’s position. For instance, a 22° halo is a circle of light with a 22-degree radius surrounding the sun (it can also form around the moon). Sometimes, rainbow spots called parhelia, or “sundogs” and “mock suns,” appear along this halo.

A circumhorizontal arc, also known as a “fire rainbow,” is a colorful sun halo that runs parallel to the horizon and can only form when the sun is above 58 degrees. The opposite of this is the circumzenithal arc, which appears when the sun is below 32 degrees.

Although none of these are technically rainbows, they share the same refraction and water properties. They also all exhibit an equally stunning brilliance.