Chapter 5 the earth has four seasons

The word "season" means "to sow", and it is derived from the Latin verb "serere".It can be seen that "season" should only be used to indicate spring --- "the season of sowing".But at the beginning of the Middle Ages, three other seasons were added to the meaning of "season", so that it lost its original simple meaning and represented the four seasons of the year: autumn, or period of growth (the root is the same as " "growth" or "dignity", which means "growth period" and "dignified person"); winter, or "wet season"; summer, which is the ancient Sanskrit term for the whole year.

Human daily life and romantic sentiments are shaped by the seasons, and besides, they have the most tedious astronomical backgrounds.Because the direct result of the earth's annual journey around the sun is the cycle of the seasons. The earth rotates once every 24 hours and revolves around the sun every 356.25 days.In order to ensure that the calendar is neatly unified, human beings accumulate 0.25 days of each year into one piece, so that a leap year occurs every four years, that is, there are 366 days in this year.But there is no leap year in the year ending with two "zeros"; but there are exceptions, that is, those years divisible by 400 are all leap years.1600 AD was a special case of the last time, and the next time is 2000 AD.

The orbit of the earth around the sun is not a perfect circle, but an ellipse.Although it is not yet a complete ellipse, it has added a lot of complicated factors to the work of human beings studying the movement of the earth. In addition, the earth's central axis and the plane between the sun and the earth do not form a right angle, but an inclination angle of 66.5°. When the earth revolves around the sun, its central axis maintains such an inclination from beginning to end, which is the direct cause of the alternation of seasons around the world. Every year on March 21, the sun shines on half of the earth's surface evenly, so on this day, the day and night are evenly divided around the world. After 90 days, when the earth moved to a quarter of its revolution, the North Pole was all facing the sun, while the Antarctic was all facing away from the sun, so the six-month day at the North Pole began, and the South Pole Then fell into a six-month-long night.When the sunny summer in the northern hemisphere arrives, residents in the southern hemisphere read a book by the stove while passing the long cold night.But while residents of the northern hemisphere are skating at Christmas, Argentines and Chileans are suffering from the scorching heat of summer, and they are sharpening their ice skates when the United States is hit by a scorching heat wave.

September 23 is the second important date for the change of seasons. This is the second day of the year when the day and night are equal across the globe.Then, on December 21, the North Pole kisses the sun goodbye, and the South Pole faces the sun, bringing harsh winter to the Northern Hemisphere and summer to the Southern Hemisphere. However, the unique tilt of the Earth's axis and the Earth's rotation aren't the whole story behind the cycle of seasons.The earth is also divided into five regions by the 66.5° tilt of the earth's axis.The equator is flanked by the tropics, where the sun's rays hit the earth almost vertically.At the poles, the angle of the sun's rays is so small that, even in summer, a beam of sunlight hits twice as much of the Earth's surface as it does itself.The north-south temperate zone is between the tropics and the poles. Here, the sunlight is not vertically irradiated, so it can warm the wider mountains, plains, rivers, lakes and seas than the tropics.

It is not possible to fully understand all of this just by explaining it in words.You go to the planetarium to have a look, and everything there can help you understand questions about the earth faster than books.But the number of cities that consider a planetarium necessary is pitifully small.Please go to the city hall to find those heads of government and tell them that you want a planetarium as a Christmas present.What is a planetarium?While they're struggling to look it up in a dictionary (maybe it'll take them 20 or 30 years to figure it out), you'd better get some apples, oranges, candles, and ink for partitions and do it yourself Alternation of seasons throughout the year.Lighting a candle with a match can bring day or night to the "South Pole" or "North Pole".If a fly landed on your home-made earth, you must not think like this: "Suppose--just suppose--that human beings are but one such bug, with nothing on the surface of a gigantic orange. Crawling aimlessly, oranges and flying insects are illuminated by a larger candle, and all this is but a small thing in the hands of a giant after dinner."

Rich imagination is of great benefit. However, please do not use it in the field of astronomy.