Nature

Light Pillars Are An Alien Illusion Made By Ice

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What do you think when you see a pillar of light? If you've grown up on a diet of sci-fi films, you probably think there's an alien abduction in progress. It turns out that pillars of light actually happen in nature, though the reason for their existence isn't a very favorable one.

Related: Olbers' Paradox Asks Why The Night Sky Isn't Blazing With Light

An Icy Illusion

Light pillars sure look like a beam of light shooting from a single source on the ground, but they're not—it's just an illusion. They happen in frigid conditions when icy clouds hover close to the Earth's surface, at a height of a few thousand feet or fewer. The clouds contain millions of ice crystals, each one a flat hexagon floating horizontally in the air like a multitude of microscopic mirrors. That's exactly how they behave: like mirrors, each one bouncing light from the ground off of its surface and into your eyes.

Related: Ball Lightning Is Still Unexplained By Science

Of course, the clouds aren't shaped like columns. So why is that what you see? The surface of every ice crystal is generally pointing in the same direction, so they're all reflecting light at roughly the same angle. If the ice crystals are too far away, that angle makes the light go past you; too close, and it comes up short. The column you see is the portion of the ice crystals that are at the exact right distance to reflect light into your eyes.

Light With A Dark Side

Of course, that leaves us with a question: where does the light come from? That's where this phenomenon stops being so natural. As physicist Les Cowley told the New York Times, "Although they look pretty, they're also a sign that someone, somewhere could do better with their lighting. You might call them light pollution pillars if you wanted to be environmental about it."

Related: Measuring Light Pollution In The Night Sky With The Bortle Scale

Light pollution may not sound like a big deal, but it can affect the environment and society in surprising ways, such as by disrupting animal migratory patterns and even increasing crime rates.

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Key Facts In This Video

  1. The first electric street lights appeared in the late 1870s. 00:30

  2. An innate attraction to light can be so strong that it can mesmerize some song- and seabirds, who are drawn to searchlights on land. 05:08

  3. Hundreds of species of night-migrating birds rely on constellations to navigate the night sky. 05:33

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