Why do the days get shorter and the nights get longer after the autumnal equinox?
After the autumnal equinox, the direct point of the sun continued to move from the equator to the southern hemisphere, and the days in the northern hemisphere began to shorten and the nights became longer, that is, the days in a day began to be shorter than the nights; The southern hemisphere is the opposite. Therefore, the autumnal equinox is also called the landing point.
At the North Pole and South Pole, on the day of the autumn equinox, the sun is on the horizon all day. After that, as the direct point of the sun continued to move southward, a six-month polar night began near the North Pole, which gradually expanded and then narrowed. A six-month polar day began near the South Pole, which gradually expanded and then narrowed.
The significance of the autumnal equinox is:
1, the autumnal equinox means that in the middle of autumn, day and night are equal in length. Another day was set up as "China Farmers Harvest Festival", which is a tribute and inheritance to the traditional "twenty-four solar terms", which is the crystallization of ancient wisdom.
2. According to the lunar calendar, "beginning of autumn" is the beginning of autumn and ends with "the first frost", and the "autumnal equinox" is exactly half of the 90 days from beginning of autumn to the first frost. The rainy season has just ended in most areas, with a cool breeze blowing gently. Wan Li is blue, the weather is clear, the autumn air is crisp, the osmanthus fragrance is fragrant, the crab is fat and the chrysanthemum is yellow, and the autumnal equinox is a beautiful and pleasant season. It is also an important solar term in agricultural production.
3. The agricultural proverb goes: "An autumn rain brings a cold", "Autumn dew divides the night, and it is cold all night". "In August, the wild goose gate opens, and the foot of the wild goose is frosty." It is not surprising that frost appears in the autumn equinox in a year when the temperature in Northeast China drops early.
On the day of the autumnal equinox, the sun is located at the longitude of the yellow meridian 180 degrees, and the sunlight is almost direct to the equator, and the length of day and night in most parts of the world is almost the same. At this time, the waiting temperature in the southern region has generally dropped below 22℃, and it has entered a cool autumn.