Why is the night sky black?

A very silly question about an obvious fact, though not everyone knows about it.

Why is the night sky black?

Surely everyone knows that the sky always has a deep black color with sparkling stars, of course on cloudy days.Have you ever wondered why the winch is black when night falls ? If you've ever done that and haven't found the answer yet, this will be the answer to this seemingly silly question.

It all began with the Olbers paradox , a theory presented by physicist Heinrich Wilhelm Matthäus Olbers in 1823, when Olbers argued that according to Sir Isaac Newton the universe was infinite and contained an infinite number of stars. This means that no matter where you look, it will meet a star whose brightness is equivalent to the brightness of the Sun. This situation is the same as when you are in the middle of a dense forest, no matter how far you look, you will be blocked by a tree. So the night should have been as bright as the day before, but it had an ink-black color. Since then, Olbers has concluded that the universe has its own limits.

However, later many experts pointed out the omission of this paradox because if placed in the context of a person standing in the forest, the closer to the edge of the forest, the more trees he will see in the middle of the forest. .This applies when we look at the sky and see it dark regardless of where we look , that is, we are in a certain area like the "center of the universe" and there will be one. somewhere in the distance far away will allow us to look up into the sky and see a half black and a half having light. Later, astronomers proved that stars in the universe are unevenly distributed - places are sparse, where tens of thousands of stars are concentrated with only a few light years between them, adding The result of this research is that the sky must be at night when there will be no dark star at all but there is no such thing.

With the advent of the Big Bang doctrine , scientists continue to add facts to this problem when learning that people's conception of the universe is still limited in time with a lot of work. the star has died billions of years ago and its light has yet to reach Earth. In addition, general relativity helped research experts discover that the universe itself is expanding at a tremendous speed and possibly forever , which causes light to travel in the lips. the cosmic field faded away, which was proved by the Austrian physicist Christian Andreas Doppler into a Doppler effect.

This effect suggests that the frequency and wavelength of sound waves, electromagnetic waves or waves in general are altered when the source of the transmission is relative to the observer. In the Doppler effect, the frequency of the wave source is not changed. To understand the cause of the Doppler effect, the frequency change, we take the example of two pitchers. A people throw the ball at B at a certain distance. Suppose the ball speed is constant and every minute B gets a fixed number of balls. If the A person slowly approaches B, the B will get more balls every minute because their distance has been shortened. So it is the number of wavelengths that changes, causing the frequency change.

In 1929, astronomer Edwin Hubble began to study the Doppler effect of light emitted by galaxies and he discovered that galaxies are increasingly moving away from its original position. This is a consequence of the Doppler effect called redshift with the light emitted by objects moving away from the observer redder. General relativity has judged the problem of red shift when photons reduce energy when exiting the gravitational field when the spectral lines in the visible light section shift towards the red spectrum due to the frequency of electromagnetic waves (of the light light, radio waves .) of galaxies, quasars or other distant objects are reduced. This explains why the light fades away through the cosmic environment and is a fairly clear answer to the question: Why is the sky at night dark?