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Why is the Sky Dark at Night?

Cheryl Mascarenhas Oct 21, 2020
The only question that has bowled me ever since childhood is why does it get dark at night? Does the sun take away all of its light only to make the sky pitch black? The answer may seem simple, but is it really so?

Moonlight is nothing but...

...sunlight reflected from its surface rendering the moon powerless to illumine the night sky.
One look into the night sky is enough to tell you that there are countless stars that are emitting light. Well, if all these stars are emitting light, why do we see only a faint glow around the stars. Why isn't this light, lighting up the sky as it really should be doing? That way, we would have fewer dark nights and more nights flooded with day-like light.
It is true then, that the universe, with its unfathomable hands, has stretched and wrapped us in dark history.
To a small child, the answer is pretty obvious, the night is dark because we are facing away from the sun. But then, would that mean the other stars are not as powerful as the sun? Or are they just too far away to brighten up the darkened and so-called night sky? Let's explore the different reasons.
Explaining the Darkness
Keeping in mind that the sun is the source of light for our planet and our galaxy, and the rotation of the planets around their own axis, we can assume that - 
✰ The sun lights up the face of the earth that comes in its light path.
✰ Due to this play of light, the other half of the earth is thrown into darkness.
✰ We can explain the darkness to be that of the shadow cast by the earth around it.
✰ This shadow extends for thousands of kilometers, due to which we get to experience a lunar eclipse once a while.
Contribution of Science
Considering that the sky is dotted with numerous stars that emit their own light, the night sky should be far from being dark. Other than lending a dim glow to the otherwise dark sky, the light from the stars hardly does anything much.
Ever wondered where all the light is going and what is it that is hindering the light from being visible? Alternatively known as Olbers' Paradox, the dark night sky is a popular and debatable cosmological problem.
Debatable because there's not just one theory to explain why the light emitted from the stars does not reach far and wide to lighten up the sky at night. Olbers' Paradox stated that if the universe is infinite and static, then the line of sight from any given angle would end at a star.
Which would mean that every part of the sky would be filled with stars so aligned that their light would merge so as to give out a bright light.
According to the Big Bang Theory, the universe as we see it now is constantly expanding, which means that the galaxy clusters are simply moving apart. The theory contradicts the assumption of an infinite and static universe, which obviously meant being able to see innumerable stars that overlapped each other to create a solid wall of light.
Astronomers came to believe that the universe itself is not old enough, and that it has evolved just about 12 to 15 billion years ago. Which means from where we are, we can see only the part of the universe that lies just about 15 billion light years away.
According to astronomers, the light of the stars beyond this mark may not have reached us as yet, which is why our sky is not as illuminated as it should be.

The Role of Atmosphere and One Bright Star

According to scientists, light as we see it during the day is reflected through the tiny molecules of air. When the earth rotates around its axis, it gives rise to the phenomenon of day and night. This means that a part of the earth is thrown into darkness merely because it is not facing the sun.
Given the fact that the sun is the only bright star in our galaxy, the bare truth is that there is no other nearby star from which the dark side of the earth receives light.
Besides, the distance between the planets are too great to bounce off the light from the sun, which is why the light emitted by the sun gets absorbed into space. This results in us experiencing dark nights and bright days.
So Says the Moon...
Ever wondered why the moon does not light up the night sky? Well, the moon, as we know it, is a mere satellite. This satellite merely reflects back the light that falls on its surface facing the sun.
Which means that it is incapable of emitting its own light. Besides, the light reflected back from its surface is not bright enough to light up the entire sky, hence emitting a faint glow - what we know as moonlight.
You must have heard of a dying star. Well, to say the least, the light that you see and believe to be that of a breaking star, or falling star, has in reality occurred several billion years ago and has reached you only at that moment.
So, in reality, the light of the thousands of twinkling stars that we see are only the facade of the light as it was million of years ago. Which means that the speed of light is finite and is not sufficient to light up space.
And with the expansion theory to support the saying, it won't be wrong at all to say that the amount of light reaching us from these far thrown stars and galaxies is dwindling all the time.
Well, if these stars are so far away from us, and if this distance is forever increasing, then it makes sense why we see the stars as emitting a faint light. Which further explains why we see a sky that is filled with darkness rather than light.