Is that a smile in the sky or are the heavens just happy to see you?
Actually, the answer is neither. On October 25, residents of the small Oxfordshire village of Leafield were treated to a rarely seen weather phenomenon that presents itself as an upside-down rainbow in the sky. But what looked like a smile was actually an event known as a circumzenithal arc.
Circumzenithal arcs, or CZAs, are not rainbows, but rather halos formed when light refracts off of ice crystals hanging in the clouds at high altitude. A similar phenomenon to mock suns or “sundogs,” CZAs form as sunlight curves sharply within plate-like ice particles, entering through a horizontal side, and exiting through a vertical side. This sharp turn cleanly refracts the beam, causing sharper definition of colors than the raindrop-based rainbows it is so often confused for. For the halo to become visible, the sun needs to be at a very specific angle, around five to 35 degrees above the line of the horizon.
Surprisingly, CZAs are actually pretty common, but due to the fact that they are always on the same side of the sky as the sun, and given their specific angle of occurrence, they are often overlooked. The other issue with catching CZAs is that they often occur within cirrus clouds, which can produce obscuring lower clouds.
But even if the phenomenon is not quite as uncommon as it seems, the undeniable whimsy of a multi-colored smile in the sky never fails to seem miraculous. One observer, Louise Longson in Leafield, said that she watched the CZA for 10 minutes until it faded away. Even though the phenomenon was brief, its occurrence managed to capture the attention of everyone from the BBC to the Daily Mirror. Sometimes it’s just nice to see nature smile, although none seem to have realized the unfortunate inverse: if CZAs are the sky smiling down on us, then aren’t rainbows a frown?
Every day, we track down a fleeting wonder—something amazing that’s only happening right now. Have a tip for us? Tell us about it! Send your temporary miracles to firstname.lastname@example.org.