Lighting up the Night

Would Aliens Do That?

A nighttime view of Beijing's city lights splashing out to space. Earth's night-time side is aglow with light splashed carelessly to space. Image courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center

We humans spend a lot of money turning our lights on at night.  We light up our houses, our parking lots, our highways, our high-rise buildings—you name it. If we build it, we light it up.  You don’t have to go to space to know that we have a love affair with illumination. That’s because light pollution is a constant on every continent. But, somehow, it seems more obvious when you see it from space.

Astronauts living and working on orbit since the dawn of the Space Age have shown us in countless images how Earth’s brightly lit cities glitter like diamonds on the night-time face of our planet. To any visitor from another planet coming to visit us, those lights have a simple message: here is a civilization that is so wealthy that it can spend money lighting up the night-time sky. Here are beings who want to advertise their presence to the cosmos.  Here is evidence of intelligent life!

Actually, our alien visitors wouldn’t have to be all that close to detect our light pollution and make some guesses about our civilization. If they had powerful enough telescopes, observers on distant planets could simply watch Earth as we turn our lights on at night. Our planet’s dark side could be detectable with a powerful enough telescope and the right kind of observational techniques.

Will alien civilizations splash their lights to space? If so, Harvard astronomers think we could use those lights to detect their existence. Credit: David A. Aguilar (CfA)

The idea is not so farfetched as it sounds. Two researchers representing Harvard University’s Center for Astrophysics and Princeton University have suggested that Earth-bound astronomers use that exact method to search for life on other planets beyond our solar system.  Those changes, if astronomers can spot them, could be due to artificial illumination, and that would signify the existence of intelligent life on distant worlds.  (You can read more about the research behind the idea here).

It’s an intriguing twist on the search for extraterrestrial civilizations, and with the pace of advancements in telescope technology, such research is not that far off in our future.  But, I have to wonder: would every civilization be so wasteful of its resources by lighting up the sky?  I suppose we’ll find that out when we spot those distant worlds and spy out their cities and roadways and parking lots and other places they choose to illuminate, just as we do here on Earth.

Want to see more images of Earth at night? Browse through the Earth from Space website. and you’ll see our planet in all its glory, as witnessed through the eyes and cameras of Earth-orbiting astronauts.