When we search for pictures of the outer space, we find them all black, and we do not know why? The answer to this question might be a little bit difficult, but we can simplify it.
On Earth, we have the Sun close to our planet and it gives us an excellent level of light so that we can see everything around us in wonderful colors. At night, we experience darkness because the light of the Sun is illuminating on the other side of the planet.
The Earth is surrounded by a gaseous envelope called the atmosphere. Apart from the layer of gases, the atmosphere contains water droplets and dust particles. As the sunlight hits these obstacles, they cause it to reflect and refract. The reflected and the refracted rays illuminate our surroundings allowing one to perceive the world in its splendid colors.
To know what happens in the outer space, we will have laser beams as an example. To see the beam of a laser, there have to be particles between the source and the destination. What we actually see is the light reflecting on those particles and ending on our retina.
Light travels in a straight line until it hits something. Outer space has some gas and cosmic dust, but no atmosphere to cause the scattering, and hence, the surrounded space appears black. Once the light hits and bounces off an object, it is the atmosphere that allows the ability to see colors in the spectrum that our eyes see.
Despite the existence of many stars in outer space, it is still dark. To know why, we will use the ambulance as an example. We know that when we hear an ambulance siren, it sounds higher pitched and louder the closer that it is, and the sound gets lower as it gets farther away from us. This is known as the Doppler effect. In the same way, the universe is expanding away from Earth. Therefore, the stars are also moving away, causing their light wavelengths to get longer. The longer the wavelength, the less visible light becomes, until there is no light that we can see.
References
tellmewhyfacts.com
phys.org
starchild.gsfc.nasa.gov
whyzz.com
livescience.com
quora.com