Have you ever looked at the sky on a clear day and thought about why the sky is blue but space is black? The question looks very simple, but the answer is one of the most interesting stories in science.The colour of the sky is not related to the sun being blue or the oceans reflecting light, as most people think. It is all about the way light from the sun travels and the way it behaves when it meets the atmosphere of the Earth.According to NASA, light molecules interact with very small air molecules in a manner that changes what our eyes see. The sky’s colours, which range from intense blue midday to fiery red sunsets, are the result of the sky’s colours being shaped by this interaction. Knowing this, we can even wonder why the sky of the Earth is so different from the blackness of space.
What colour is sunlight really
The sunlight appears white to our eyes, but it is actually a combination of several colours. These colours are red, orange, yellow, green, blue, indigo, and violet. These are the colours that make up the visible spectrum. This is very obvious when the sunlight goes through a prism or after rain when there is a rainbow in the sky. Every light colour is a wave. Certain waves are long and smooth, while others are short and rough. The waves of red light are longer, whereas those of blue light are very much shorter.
How light behaves in the atmosphere
Light is generally straight-line until it hits an object. When sunlight comes into the atmosphere of the Earth, it encounters very small molecules of gases such as nitrogen and oxygen. These molecules are able to reflect light, bend it, or scatter it in different directions.Scattering is the main reason why the sky is blue. Blue light has shorter waves, and this is the reason why it is more easily scattered by the small gas molecules in the air. When sunlight comes into the atmosphere, blue light is scattered in all directions. The sky appears blue most of the time because the scattered blue light comes to our eyes from every part of the sky.The other colours, such as red and yellow, have longer waves and are scattered very little. They mainly keep going in a straight line.
Why the sky looks lighter near the horizon
When you look at the sky near the horizon, it is very often of a very light blue or even white colour. It takes place because a longer portion of air is passed through by the sunlight that comes from that direction. When light goes through more atmosphere, blue light is scattered several times. The multiple scattering mixes the colours again; thus, the sky looks less blue and more white.Besides this, light is coming off the Earth’s surface, like land and water. This emitted light is mixing the colours too, mainly close to the horizon.
The science behind red sunsets
Sunsets are also a stunning consequence of light scattering. A red sun is a classic example of such an event. The sun near the horizon or soon after it has set is seen as intense red or orange.The reason for that is the light from the sun must pass the longest path. Blue light is scattered in the atmosphere; therefore, mostly red light reaches the observer, and the sun looks red. In this process light is scattered into different directions, and the light coming directly from the sun is deprived of blue light. This process is called the scattering of light.When the sun is low in the sky, its light has to travel through a much thicker layer of atmosphere to reach your eyes. Most of the blue light has already been scattered away by the time it gets to you. What you see are the longer wavelengths, mainly red, orange, and yellow. That is why sunsets are often red or golden. If there is dust, pollution, or smoke in the air, the effect becomes even more powerful. The tiny particles are better at scattering blue light, thus making the sun seem to be red. After, the pulsing red sun can be hidden behind the dust and smoke, and the sunset can be as breathtaking as ever and is still there but no more visible. So in case you want to go for a walk and view the empyrean fireworks, it might be
Is the sky blue on other planets?
The reason the sky looks different colours on other planets is that their atmospheres vary. Take Mars for instance. Its atmosphere is very thin and is made up of about 95% carbon dioxide and is also contaminated with very fine dust particles.On Mars, the sky looks orange or red during the day because dust particles scatter light in a different way than air molecules do on Earth. However, a very surprising thing is happening at sunset time on Mars. The sky next to the sun becomes bluish-grey, which is a complete reversal of what we observe on Earth.
Why space is completely black
Now the most intriguing part follows. Why is space black if the Sun is shining all the time?The answer is quite straightforward. Space is without atmosphere. Since there are no air molecules or particles, there is nothing to scatter the sunlight. Sunlight is a beam of light that comes from the sun. If you look straight at the sun, you see a very bright white light. However, if you look in another direction, the light that is scattered does not come to your eyes. As there is nothing in space to scatter the sunlight, the sky is black even during the day.A simple idea with a big impactSo, the blue sky we enjoy every day exists only because of Earth’s atmosphere. It protects us, supports life, and creates the beautiful colours we see above us. Without it, our sky would look just like space, dark and empty.Next time you see a blue sky or a red sunset, remember that you are watching light waves dancing through the air. It is a reminder that even ordinary sights can have extraordinary science behind them. Go to Source
