You are not alone if you have ever wondered where your tan comes from when you are sitting on the beach or around a pool.
Astronomers and physicists have been hard at work figuring out the problem as well – and the results of their research come as a bit of a surprise.
If you believe your tan comes from sitting out in the sun, you are right and wrong.
A sun tan comes from a continuous bombardment of photons from space.
Most of those photons come from the sun – either as direct light or as reflected light from space dust and other particles floating around the solar system.
But others come from a lot farther away.
Photons from other galaxies
Scientists from the International Centre for Radio Astronomy Research (ICRAR) measured light hitting the Earth from outside our galaxy.
Photons that have travelled millions of light years from other galaxies and black holes account for some of a tan. Some photons have travelled across space for billions of years from the Big Bang, but they are too weak to help deepen a tan.
The research also detected low-level radiation in some photons, but the dose is far too low to have any impact on health even after a lifetime of exposure.
“Most of the photons of light hitting us originate from the Sun, whether directly, scattered by the sky, or reflected off dust in the solar system,” said ICRAR project leader Simon Driver.
“However, we’re also bathed in radiation from beyond our galaxy, called the extra-galactic background light.
Why the beach is good for you
“These photons are minted in the cores of stars in distant galaxies, and from matter as it spirals into black holes.”
Although we cannot feel the billions of photons that hit our beach bodies every second we are out enjoying the sun, that feeling of relaxing and being at one with the universe is not such a flippant idea after all.
Meanwhile, a separate study by a team from Michigan State University in the USA concluded that spending some time relaxing on a beach is good for your mental health.
The scientists believe blue light from the sky and sea calmed the brain – and even switching a screen saver on a computer to a beach scene helped.