Which side is black first, Zhenjiang, Jiangsu or Beijing?

The vernal equinox and autumnal equinox are two solar terms, and Zhenjiang is the first to get dark.

Because Beijing is in east longitude 1 16 and Zhenjiang is in east longitude 1 19, there is a difference of 3 between Zhenjiang and Beijing. On the earth, the solar time of 3 degrees is 360/24 hours /= 15 degrees, and 15 degrees is one hour, so 3 degrees/15 degrees = 12 minutes.

In other words, Zhenjiang is 12 minutes earlier than Beijing.

We know that the sun rises in the east and the earth rotates from west to east.

Assuming that the sun does not move, the sun shines directly on the equatorial line at the vernal equinox and autumnal equinox, and the earth rotates from west to east, then the time to see the sun in the west is later than that in the east, and the time to see the sun in the east is earlier. See the sun early, get dark early.

At the vernal equinox and autumnal equinox, the whole world is divided equally between day and night, except the Antarctic and the North Pole.

In addition to the vernal equinox and autumnal equinox, latitude should also be considered.

In the Arctic Circle, six months in a year are day (called extreme day) and six months are night (called extreme night). So in the northern hemisphere with high latitude, there are more sunshine hours in summer than in the south. Compared with Zhenjiang, Beijing's north latitude is high, at 40, while Zhenjiang's is low, at 31. The sun crosses the equator to the north until the summer solstice. The higher the north latitude, the longer the illumination time.

Except for the two solar terms of vernal equinox and autumnal equinox, where it gets dark early may be a complicated calculation problem.

According to records, taking Beijing as an example, on June 22nd, 2007, the sun rose at 4: 13, set at 20: 19, and illuminated at 16 hours and 6 minutes. The 22-day illumination time in Haikou, Hainan Province is 14 hours 10 minute, Shanghai is 15 hour 07 minute, and Mohe, Heilongjiang is 18 hour 38 minute.

"Quality jelly" raises a very good question.