How Does The Sun Create A Pillar Of Light In The Sky?

The right weather conditions can send pillars of light shooting up across the sky. Find out how nature forms its own spotlights.

Many people have been walking home in the evening when they turned to see the setting sun seemingly shooting a beam of light directly up into the sky. I imagine fewer people have seen the same with the rising sun, but under the right conditions it can do the same. The beam can be diffuse or intense. It may be concentrated at the bottom and trailing off as it rises higher, or it can fade and brighten in unexpected places. It can even come from artificial light sources. Always, though, it forms a straight pillar rising up from the sun.

Two things are needed to form a sun pillar; a strong light source which is close to the ground and a sky full of ice crystals. In a past post on Io9, we've shown how hexagonal ice crystals in the air can bend light, making it appear that there are multiple suns, or sun dogs. Sun pillars happen when the sunlight strikes these crystals from a different angle. Instead of going through the body of the crystal, reflecting off its sides, the light hits the bottom of the crystals and reflects back down to the earth.

Instead of escaping upwards into the sky, the sunlight gets reflected back down to earth. From an earthbound person's perspective, the light climbs upwards in a pillar. In reality, we're only seeing it because it got knocked back down to us.

[Via Optics, The Weather Doctor, and Atmospheric Optics.]