Why is the night sky dark? Detailed answer

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Why is the night sky dark? Detailed answer

Big encyclopedia for children and adults

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Why is the night sky dark?

If the universe were infinite in space and time, then in any direction there would be some star on the line of sight. The entire surface of the night sky would have to appear dazzlingly bright, like the surface of the sun.

The contradiction of this statement with what we observe in reality is called the Olbers-Shezo paradox. This paradox cannot be explained within the framework of the theory of the stationary Universe. However, it is easy to eliminate, given that the universe originated in the so-called Big Bang and that its age is "only" 13,7 billion years.

The most distant objects that we can see are no more than 13,7 billion light-years away from us, and the light from the more distant ones has not yet managed to reach us (the speed of light, as you know, is not infinite and is 300 kilometers per second). That's why the night sky is dark.

Author: Kondrashov A.P.

Random interesting fact from the Great Encyclopedia:

What is tin-lead alloy?

First, an alloy is a metal that results from mixing several metals during smelting. The basis of the tin-lead alloy is tin. It is usually mixed with lead in the following proportions: 6 or 4 parts of tin to 1 part of lead. Such an alloy has been produced for thousands of years, although it is difficult to give a more precise date. It is said to have been known to the ancient Chinese, Egyptians and Greeks. The ancient Romans also made it.

Usually the mention of the tin-lead alloy is associated with England, and there is a reason for this. In Cornwall there were mines with deposits of high quality tin. England has been smelting it since ancient times, and tin from Cornwall has been used to make such alloys in other parts of Europe. Tin-lead alloy was used for three main purposes: for the manufacture of church utensils, for domestic use and for public use. Communion bowls made from a pewter-lead alloy have been used in church services in England since the Middle Ages. In England, this alloy began to be widely used for the manufacture of plates and cups.

But over time, the rich began to prefer silverware, and the middle classes used a tin-lead alloy instead of silver.

In France, this alloy has been used to make glasses and goblets, plates, salt shakers and pots since the XNUMXth century.

In Germany, the industrial production of tin-lead alloy arose in the XIV century, and almost at the same time it began to be smelted in Belgium, Holland, Switzerland, Russia and the Scandinavian countries.

In the United States during the early colonial period, it was used more for household purposes. Some items date back to the 1750th century, but the largest amount of alloy was produced between 1850 and 1000, when it was used to make any household utensils. Tin-lead alloy was smelted in China, Korea and Japan more than XNUMX years ago.

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foam paper 06.06.2000

Styrofoam is widely used for packaging fragile products - a porous plastic used to make packaging inserts for boxes with equipment and balls or flakes poured into such boxes to soften shocks. However, the synthesis of styrofoam consumes a non-renewable raw material - oil, gases that are dangerous for the Earth's ozone layer are used in its production, and the used packaging practically does not decompose, accumulating in nature.

The German inventor Friedrich Pries from Hamburg founded a small company that produces foamed packaging material from waste paper using the technology he developed. Waste paper is finely cut, then ground into individual fibers, which are mixed with starch.

Granules are pressed from this mass. They are subjected to high pressure in a sealed apparatus with superheated water vapor, and then the pressure is abruptly released. The granules foam, forming porous balls that absorb shocks better than styrofoam.

Packing inserts are also obtained, only the paper pulp is preliminarily poured into molds. This material is cheaper than styrofoam and quickly decomposes in a landfill by microbes and fungi.

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