NASA’s New Horizons probe gives us best estimate of deep space’s darkness | Space

Space looks black, but just how dark is it?

It’s a deceptively simple question that has puzzled astronomers since the 1960s. Now, thanks to data from NASA’s New Horizons probe, they have arrived at the best-yet estimate of how dark — or rather, bright — deep space is: 100 billion times dimmer than the sunlight we see on Earth.

That’s the amount of ambient, universe-permating glow from the births and deaths of trillions of galaxies and their countless stars ever resided in our universe. This vanishingly faint light is called the cosmic optical background (COB), and can be thought of as the visible equivalent of the cosmic microwave background (CMB) radiation, the light left over from the universe’s creation.

“If you hold up your hand in deep space, how much light does the universe shine on it?” study lead author Marc Postman, an astronomer at the Space Telescope Science Institute in Baltimore, said in a statement. “We now have a good idea of just how dark space really is.”

Precise measurements of the COB allows astronomers to study how and where galaxies and stars formed across the universe’s 13.8-billion-year history. But the remnant glow is so imperceptible that even advanced telescopes struggle to distinguish it from unrelated light sources in the inner solar system, including sunlight scattered by the swarm of debris around Earth and countless specks of…