Why is the sky in the night Black???...

[Koni]

The Hubble Telescope has shown that in the darkest places of the Univerce there are old Galaxies!!!...

So, is the Black Night Sky only an Illusion of our Eyes???...

( IF we had Eyes like the Telescopes would the sky be full of sunlight???...)

Thank You...

[swansont]

This is Olbers' paradox

https://en.m.wikipedia.org/wiki/Olbers'_paradox

Short answer is that because the visible universe is finite, owing to expansion, there are a finite number of stars to see. And intensity drops off as the square of the distance, so far awaybstars are dim, even though there are a lot of them.

telescopes are able to gather more light, owing to area and exposure time, which is why Hubble can see so much 

[Strange]

This is a really good question! This is called Olber's Paradox. And the reason the sky is dark is because the universe is expanding so at some distance there are no more galaxies to see.

https://en.wikipedia.org/wiki/Olbers'_paradox

[Sensei]

2 hours ago, Koni said:

The Hubble Telescope has shown that in the darkest places of the Univerce there are old Galaxies!!!...

They are redshifted... no longer in human visible spectrum of light..

https://en.wikipedia.org/wiki/Redshift

Add to it inverse-square law.

https://en.wikipedia.org/wiki/Inverse-square_law

[math]I = \frac{I_0}{4 \pi r ^2}[/math]

 

Quote

Why is the sky in the night Black???...

Black means lack of photons at visible spectrum between 400 nm .... 700 nm..

Black materials are emitting photons in IR spectrum depending on their temperature. You can see them using IR camera.

Analyze where is peak will tell temperature (that's how IR thermometers are working (from distance))

https://en.wikipedia.org/wiki/Wien's_displacement_law

 

 

Edited December 31, 2017 by Sensei

[Koni]

Thank you all for your correct answers!!!...

But with light I don't mean only visible for us Humans Eyes light but light in General...

 

[Mordred]

Olber's paradox still applies

[Strange]

3 hours ago, Koni said:

Thank you all for your correct answers!!!...

But with light I don't mean only visible for us Humans Eyes light but light in General...

In physics, "light" usually refers to all electromagnetic radiation. Because of expansion, there is a distance beyond which light is able to reach us - it would take longer than the age of the universe to arrive. As a result, there are a finite number of stars in the observable universe.

[Koni]

Thanks !!!