How was the calendar invented? Detailed answer

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How was the calendar invented? Detailed answer

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How was the calendar invented?

When man began to grow corn and harvest, it was noted that the time of sowing came at the same time every year. People began to count how much time passes between crops. This was the first human attempt to determine the number of days in a year!

The ancient Egyptians were the first to determine the length of the year with great precision. They knew that the best time to plant crops was after the annual floods of the Nile. The priests noticed that 12 full moons pass between floods. After counting 12 "months", it was possible to determine the beginning of a new spill.

But it wasn't accurate enough. The priests also noted that every year, at about the same time as the flood began, a bright star appeared in the sky before sunrise. We counted the days between these events - it turned out to be 365 days. It was 6000 years ago, and before that no one knew that there were 365 days in a year. The Egyptians divided the year into 12 months of 30 days, adding 5 extra days at the end of the year. Thus the first calendar was born.

Over time, the calendars were based not on the new moon (lunar calendar), but on the number of days - 365,25 - needed by the Earth for a complete revolution around the Sun (solar calendar). The extra quarter of a day began to interfere more and more. Finally Julius Caesar decided to fix it all. He ordered to count 46 BC. e. consisting of 445 days to "adjust" the calculations, and each subsequent year had to consist of 365 days, with the exception of every fourth year. This fourth year - a leap year - will consist of 366 days, taking into account a quarter of a day of the previous three years.

But over time, they discovered that religious holidays (Easter and others) did not coincide in days in each subsequent year. Added too many "extra" days. In 1582, Pope Gregory XIII issued a decree that reduced the year 1582 by ten days. For more accurate chronology in the future, a leap year falling in the last year of the century will only be in a year that is divisible by 400. Therefore, 1700, 1800 and 1900 were not leap years, and 2000 will be a leap year!

This system is called the Gregorian calendar and is used all over the world on a daily basis, although many religions use their own calendars for their own purposes!

Author: Likum A.

Random interesting fact from the Great Encyclopedia:

What is acid?

Often newspapers publish reports that someone has been burned with acid. Indeed, we all believe that acid is a very dangerous liquid that burns the skin and burns through tissue.

But this applies to a small amount of acids. The acids that are present in foods are essential for our health. Other acids are used in the manufacture of medicines, paints, cosmetics and industrial products.

There are many types of acids, but they can all be divided into two classes - inorganic and organic acids. Let's get acquainted with the most significant representatives of each class.

Sulfuric acid is widely used in industrial production. It is harmful to the eyes and causes skin burns. Another strong acid is hydrochloric acid. It is obtained by combining sulfuric acid and sodium chloride. It is used in the production of various chemical compounds and in the cleaning of metal surfaces. The human body produces a small amount of weak hydrochloric acid, which is used in the digestion of food.

Nitric acid is also a strong acid and is also harmful to the eyes and skin. Boric acid, on the other hand, is a weak acid. It occurs naturally in Italy. It is used in the manufacture of ceramics, cements, and cosmetics. Sometimes it is used to fight germs, but it is not effective enough. Carbonic acid is obtained from carbon dioxide, some of it is added to fruit drinks. Arsenic acid is used in the manufacture of disinfectants.

Organic acids are not as strong as inorganic acids. Acetic acid is found in vinegar, it can be obtained from the fermentation of apple cider. When sugar is formed in milk, lactic acid is formed. It oxidizes milk but is also used in cheese making.

The use of amino acids contributes to maintaining good health, we get them with protein foods. Oranges, lemons and grapefruits contain ascorbic acid - this is the chemical name of vitamin C. Nicotinic acid is present in the liver, poultry meat, beef, it prevents the development of skin diseases.

As you can see, this difficult story about acids can be continued for a long time. Some of them are dangerous to humans, but useful in industry. Others are necessary for human life support and are present in food products. There are acids that are produced by our body and are necessary for its life.

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RF-powered cardiac implant 14.09.2012

A team of Stanford engineers has unveiled a miniature implantable heart device powered by radio waves instead of batteries. The device measures only about 0,8 mm and could fit on the tip of a needle.

The results have been published in Applied Physics Letters. Scientists have demonstrated the operation of a millimetric device implanted in the chest to a depth of about five cm directly on the surface of the human heart. Until now, such a depth was considered inaccessible to radio waves. Engineers believe that this is only the first step in the production of wireless implants. In addition to heart implants, these can be endoscopes, pacemakers, brain stimulators and other medical devices where small size and power are critical.

Implants have revolutionized medicine in their time. Currently, such devices - pacemakers, cochlear implants, etc. - provide the proper quality of life for hundreds of thousands, if not millions, of patients. But in the process of designing these devices, one has to solve complex engineering problems. The size of the nutrient element and the time of its operation are critical. For example, in a pacemaker, the battery occupies up to half of its total volume. And when the battery runs out, the person needs a new operation. The ability to receive energy through radio waves solves both of these problems.

According to existing mathematical models, it was assumed that high-frequency waves do not penetrate too deeply into the tissues of the human body. Because of this, there have been no attempts to create such implants so far - low-frequency transmitters and, consequently, large antennas would be required. Too big to be implanted in the body. However, a team of scientists led by Ada Poon, a professor of electrical engineering at Stanford University, has refuted this notion.

Electric waves really quickly dissipate in tissues, but radio waves, with proper selection of frequencies, can penetrate to great depths. By revising the models, Ada Poon and her co-authors showed that in a certain high-frequency range, the power of the transmitted energy increases by about ten times. This means that the receiving antennas can be 10 times smaller, which means that there will no longer be problems with the implant due to size. At the same time, the optimal frequency at which the device operates is capable of producing about 50 microwatts of energy, which significantly exceeds the needs of existing pacemakers - 8 microwatts.

The developers have applied for a patent on the design of the wireless implant antenna and plan to continue working to create the most efficient devices that meet the sanitary standards set by the IEEE.

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