Why does space appear black to an astronaut?

We all want to witness the universe beyond just the planet we live on.

From earth whatever we see outside is the minutest fraction of what actually lies in the great beyond.

However, we have been grateful enough to see so many pictures and videos of what space actually looks like.

And few lucky people, or to be precise, highly trained people have even gotten the honor of traveling there.

One of the major differences we notice is in how the view above looks to us and looks to astronauts in space.

Why is the sky blue on Earth?

To us on Earth, the sky looks like a wonderful shade of blue.

Sometimes the colors may differ but the color we mostly witness is blue, as we have aptly named sky blue.

Let us first understand why we on this planet witness the sky as blue. 

When sunlight reaches the Earth's atmosphere, it is scattered in all directions by all the gases and particles in the air.

Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. 

Blue is scattered more than the rest of the colors as it travels in shorter, smaller waves as compared to the other colors.

This is why we see a blue sky most of the time.

What happens closer to the horizon?

Closer to the horizon, the sky fades to a lighter blue or white.

The sunlight reaching us from low in the sky has passed through even more air than the sunlight reaching us from overhead. 

As the sunlight has passed through all this air, the air molecules have scattered and rescattered the blue light many times in many directions.

It is also important to remember that the surface of Earth has reflected and scattered the light. All this scattering mixes the colors again so we see more white and less blue.

To summarise, sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. 

Blue light is scattered more than the other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

Light and black holes

Let us also understand the concept of a black hole in space in context to light and darkness in space.

A Blackhole is created when neutron stars collapse into itself causing an extremely dense and highly concentrated area.

This area made by a massive star is called a black hole. It is such a dense state that even the speed of light cannot help it in escaping the region.

The visible light in the area slowly starts reducing as we reach the outer circle or the event horizon of the black hole. Many pictures have been clicked and created of this galactical phenomenon. The outer space we know today is said to be covered with black holes all over.

A black hole is known to have very intense gravitational waves. Detection of gravitational waves from black holes which merge was successfully noticed on September 14, 2015 for the first time.

Even though we do know black holes are bodies that do not allow any light to emit. there isn't still any direct correlation between how we perceive space as black and how these bodies exist.

Why do astronauts in space see space as black or dark in color?

We also need to have some additional information to understand the whole cause behind this. The wavelength of blue color is 450nm with a frequency of 6.66Hz

The scientific definition of wavelength is given as the distance between successive crests of a wave.

We also must understand the concept of the frequency of waves.

The frequency of waves can be defined as the rate per second of a vibration that constitutes a wave, that is either in a material(as in sound waves) or in an electromagnetic field(as a light ray).

Lastly, what is the scattering of light?

Atoms or molecules which are exposed to light absorb light energy and then re-emit light in different directions with different intensity. 

This phenomenon is called the scattering of light.

Furthermore, the scattering of light in a colloid or a very fine suspension is known as the Tyndall effect.

The reason the sky appears blue is the exact reason or the lack of reason as to why space looks black.

Due to the lack of atmosphere in space, light does not get scattered into its constituent colors in space.

On earth, due to the atmosphere, the scattering of light takes place. This is why the sky appears dark instead of blue to an astronaut in space.