Fall, also known as autumn, the third season of the year, the transition season from summer to winter, the northern hemisphere is from September to November, the southern hemisphere is from March to May, and the astronomy is from autumn to winter. Meteorologists study the phenology criteria: after the heat, the average temperature in the five days is stable below 22 degrees, even if it enters the fall, when it is below 10 degrees, the fall is over. The most obvious change in the natural landscape is on the trees. The city will start to clean a lot of fallen leaves, and the mountains will flood into the tourists who watch the red leaves. The direct point of the autumn sun gradually moves southward from the northern hemisphere. After the autumn equinox, it crosses the equator and the sun shines directly into the southern hemisphere. From the northern hemisphere, the angle of the sun is getting lower and the gap between day and night is smaller. In the autumn equinox, the night and night are the same. In the fall, the distance between the Earth and the Sun is getting closer. From the ecliptic plane, the sun is on the background of Leo, Virgo, and Libra.