Why is outer space dark

Since red light has a wavelength nm about 1. This scattered blue light goes out in all directions through the atmosphere and comes to us from throughout the sky during the day. However, when the sun is near the horizon sunlight must pass through a thicker amount of atmosphere than when it is overhead.

As the light travels the longer distance through the atmosphere most of the blue light gets scattered out and the light that remains has proportionally more orange, leading to the beautiful sunrises and sunsets we are often blessed to see.

These scattering effects are not however constant. All of these mechanisms can enhance or diminish the beauty or color of a sunrise or sunset. In space or on the Moon there is no atmosphere to scatter light. The light from the sun travels a straight line without scattering and all the colors stay together. Looking toward the sun we thus see a brilliant white light while looking away we would see only the darkness of empty space. Since there is virtually nothing in space to scatter or re-radiate the light to our eye, we see no part of the light and the sky appears to be black.

If you were on the Moon, which has no atmosphere, the sky would be black both night and day. You can see this in photographs taken during the Apollo Moon landings. So, now on to the harder part - if the universe is full of stars, why doesn't the light from all of them add up to make the whole sky bright all the time?

It turns out that if the universe was infinitely large and infinitely old, then we would expect the night sky to be bright from the light of all those stars. Every direction you looked in space you would be looking at a star.

Yet we know from experience that space is black! This paradox is known as Olbers' Paradox. The reasons for the additional brightness, which remain unknown, will be the focus of future studies. Until then, one thing seems likely: Space could very well be more "charcoal" than pitch-black. Tiffany Means is a meteorologist turned science writer. Tiffany has a bachelor's degree in atmospheric science from the University of North Carolina, Asheville, and is earning a master's in science writing at Johns Hopkins University.

Olbers wondered: If the universe is infinite, and there are an infinite number of infinitely old stars, why isn't the light from those stars visible from Earth? If it were, the night sky would be bright, not dark. By the end of the 19th century, the idea of an infinite universe had been largely abandoned—something which was anticipated by Edgar Allan Poe in his essay, Eureka , where he wrote :. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all.

In other words, Olbers' Paradox is resolved with the assumption that the universe has a finite age something which is supported by the Big Bang Theory , that the speed of light is finite, and thus the observable universe has a horizon beyond which we can't see the stars. Fifty years later, Lord Kelvin used math to prove that in a finite universe, or one in which stars were born and died, the night sky should be dark.

There are other contributing factors to the darkness out there.