How Dark Is Deep Space? NASA’s New Horizons Mission Finally Reveals the Answer | Space

To paraphrase the great Nigel Tufnel, when you look out into deep space, far away from any stars, how much more black could it be? And the answer is, at least some, but not much. Researchers managed to measure the light level that pervades all of the universe, a leftover glow from when everything was brand new, bright, and hot, allowing them to get a true sense of how dark it really is out there.

While it would seem logical that deep space is pitch black, there is ample evidence of radiation in space, including gamma rays, microwaves, and infrared. While not visible to the human eye, these rays do count as light. Thanks to space telescopes like Hubble and James Webb, astronomers have had a rough estimate of the amount of background visible light in the universe, a metric known as the cosmic optical background (COB), which is basically the sum total of all light generated over the course of the universe’s 12.6 billion years.

But determining exactly what level this is has been a major challenge. Measuring the exact level of the COB is impossible from Earth or its immediate surroundings, owing to sunlight scattered by interplanetary dust.

To get around this problem, a team of astronomers from the Space Telescope Science Institute and numerous U.S. universities turned to one of humanity’s most distant tools. NASA launched the…