Why space is dark and black when the sun can light up the earth

Well, we have all seen how beautiful the sun rise and sun sets look with the sky changing its colors from a reddish orange tint to the bluish one and back to reddish during sunsets. All this happens because of the sun light which enters the earth. The big golden star Sun is said to be around a distance of around ~150 million kilometers from our planet Earth. And it takes around ~8 minutes for the sun light to reach our planet Earth. 

How amazing it is that a star so far away from our planet can still send light to brighten up everything around right? Now, let's think if a light source so far away can brighten up a planet why does the space through which the light waves travel are still dark? Why the space always look dark or black? It should have been lightened up even more right? Also space is said to be filled with billions and billions of stars which give out the light of their own. So why is the space not completely filled out with light ? Let's find out!!

 The main reason why we are able to see our blue sky is because of the atmosphere that we have! How light interacts with the atmosphere. You can read about it in detail over here.

Why sky is blue and sunsets are red?

This will put some light on the whole phenomenon of what is happening when sun enters our planet.

To summarize, when sun light enters our planet, it interacts with the atmosphere which has presence of different gases. This results in scattering of the light when light waves interacts with the different atoms and molecules present in the gases. Scattering happens when any atom, molecules or even dust particles do not absorb but reflect or refract the light waves. Depending upon how the light waves are scattered decide on the color of the sky at a specific time of the day.

Now we have to understand that the main key word here is atmosphere. It is our planet's atmosphere that we are able to see the beautiful sun rise and sun sets. Coming back, light will always travel in a straight line until and unless it will hit something which can lead to scattering.

Agreed that there are some cosmic dust particles around in the space however its not enough to be creating a full brightness around the space. Classic example can be taken of Moon which has almost no atmosphere so the sun light directly lands on the surface of the moon. The light from the sun travels in a straight line without scattering and all colors stay together. So, if one looks in the sky while standing on the surface of the Moon you will only see black sky with stars.

Also, why if the universe is filled with billions and billions of stars then why does it not brighten up the space? Well this is called as Oblers Paradox because of the contradiction between our expectation that the space should be bright but is known to be black from our experience. There have been many explanations to resolve this paradox. One which sounds reasonable focusses on the age of the universe we are in. It is said that our universe is only around ~15 billion years old which would mean that we can only see objects as far away as the distance light can travel in 15 billion years (light travels in a constant speed) Also the light from the stars further away is yet to reach us.

Another explanation would be the ever expanding universe, when a source of light is moving away from us the wavelength of the light becomes longer and longer( more red and darker red in color). The more farther the light source becomes the more it moves away from the visible light. So the light becomes less and less intense (more dimmer) for us until it becomes totally non existent and this absence of light is what we perceive as dark and black.

There might be another question that when sun is hot and if we can feel the heat of the same why the space is said to be chilly and cold. The answer would be the same. When the light waves get in touch with the molecules present in Earth's atmosphere it tends to interact with the molecules and transfer the heat to the molecules thereby causing them to heat. These molecules when get in touch with other molecules tend to heat them up as well.

Now this will only happen with the molecules which tend to be in path of the sunlight. As we spoke about earlier, the vastness and a relative empty space with fewer molecules make it more chilly. 

So, in short ever expanding universe, not enough matter to scatter light can be understood to be one of the reasons why we see space as dark and black. And not just dark and black but also chilly and cold. Science as we know is ever evolving with different discoveries and advancements made over the time. Maybe we would know or have much better explanation on this few years down the line. Maybe some curious mind will find more answers to this

Until next time, keep shining the light on the curious mind! 

Wait, before you go.. ever wondered why we cannot see in the dark? Find out more below

Why we cannot see in the dark?

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