In winter, the operating hours of gymnasiums are shortened because the movement of the direct point of the sun makes the solar radiation energy received by the earth's surface change with time and place. This change can be reflected by the change of the length of day and night and the height of the sun at noon. The length of day and night reflects the length of sunshine time; The midday sun height is the maximum sun height in a day, which reflects the intensity of solar radiation. The combination of the two can qualitatively represent the amount of solar radiation energy at a certain time and place.