Part of Your Suntan Is Intergalactic
published during a full moon.


Credit: ESA/Hubble/NASA/N. Grogin

When you step into sunlight, you’re blasted with tiny photons. Now research suggests a few of those particles are so ancient, they’ve been traveling for billions of years.

That means that a very small, but very cool, part of your tan qualifies as intergalactic.

Most of your summer color is, obviously, from our home star, the sun. But Earth is a floating orb that receives radiation from all over the universe. Photons are tiny energy packets, and if you (or your sleep-prone pet) have ever napped in a sunbeam, you bathed in about sextillion photons of light per second.

But the sun isn’t our only radiation source: When you set foot outside during the day or nighttime, about 10 billion photons per second hurdle at you from deep space, according to a study published in the Astrophysical Journal. 

Those rogue photons are a minuscule part your suntan — ten trillionths, to be exact. That includes particles lobbed from far-away stars, black holes, and other sources of extragalactic background light, a blanket of all the ultraviolet, optical and infrared photons ever emitted in the universe.

Remnants of the Big Bang reach us, too.

That’s not reason to worry, though. The researchers examined wavelengths from photons both harmless and harmful, and astrophysicist and lead author Simon Driver assured that the radiation would only be harmful if we marinated in those intergalactic photons for trillions of years.

The researchers culled the data from a few surveys, most notably the Galaxy and Mass Assembly (GAMA), which has so far catalogued about 300,000 galaxies. Here’s a mind-blowing flythrough of just one of GAMA’s fields: