With the Beijing Winter Olympic Games approaching, the medal design of this winter Olympic Games and winter Paralympic Games has also attracted the attention of many people. According to the design team, the front pattern of the medal originates from the traditional string jade, while the concentric rings and 24 points engraved on the back are taken from the ancient astronomical map, which not only symbolizes the vast starry sky, but also symbolizes that the Winter Olympic athletes are as bright as stars. So, which ancient astronomical map is taken from the back of the medal, and what wonderful and interesting knowledge of ancient Chinese astronomy is contained in it? The design team revealed that the design inspiration of the medal comes from the "seven balances and six rooms diagram" in the zhoupi Suanjing, which is mainly used to describe the relationship between the annual apparent motion law of the sun and the change of solar terms, and reveal the origin between astronomy and calendar. Different from the five circles on the medal, there are seven concentric circles equally spaced on the "diagram of seven balances and six rooms". Each circle is a "balance", and the balance is called "between". Each balance represents the orbit of the sun in different periods of a year. On the Qiheng diagram, the outermost circle with the largest radius is the outer balance. At this time, the solar orbit is farthest from the observation point, indicating the winter solstice and cold weather. The innermost circle with the smallest radius is the internal balance. At this time, the solar orbit is closest to the observation point, indicating the summer solstice and hot days. From the winter solstice to the summer solstice, the five balances in the middle represent the solar orbit circle during the five solar terms of great cold, rain, spring equinox, grain rain and Xiaoman. From the summer solstice to the winter solstice, the five scales in the middle represent the solar orbit circle of great heat, slight heat, autumnal equinox, frost fall and light snow respectively. From external balance to internal balance, and then from internal balance to external balance, the two stages are divided into 12 equal parts, which together are 24 solar terms. You may wonder, is the Qiheng diagram a "rough" division of the distance and distance of the sun made by the ancients simply based on the temperature difference in the absence of modern astronomical knowledge? The answer is not so. The reason is that the Qiheng diagram is not a plane concentric circle, but a coaxial circle parallel on the spherical surface. This axis runs through the north celestial pole, that is, the earth's axis of rotation. The ancients didn't know that the change of day and night and the change of seasons were caused by the earth's rotation and revolution when building the universe view. They imagined a celestial sphere concentric with the earth and with an infinite radius. The sun, moon and stars are all located on the spherical surface, rotating from east to west with the north celestial pole as the center, as the ancient saying goes: "the polar stars do not move, but the stars arch it". It can be seen that the Qiheng diagram does not mechanically divide the height of the sun on the plane, but depicts the trajectory of the sun moving between different scales along the spherical surface in a year. At the same time, in apparent motion, the sun rotates around the polar axis once a day, so there are days and nights. If the apparent path of the sun's movement between different scales in a year is connected, the "ecliptic" of the sun's rotation on the celestial sphere will be formed. In the west, the stars in the zodiac are divided into twelve constellations, and in ancient China, they were named 28 constellations. They surround Polaris, rising and falling day after day. Divide the ecliptic 24 equally, and each arc of the sun is a solar term. Because the sun does not run at a uniform speed, the span of each solar term is not necessarily equal. At the same time, there is a corresponding relationship between "Qiheng and Liujian" and the division of five zones on the earth. The middle balance corresponds to the equator, and the inner balance and outer balance correspond to the Tropic of cancer and the Tropic of cancer respectively. Twenty four solar terms is a great creation in the field of Ancient Agronomy in China. For thousands of years, it has played an important role in indicating Phenological Seasons and guiding agricultural production. The astronomer Luo xiahong of the Western Han Dynasty determined the date of the 24 solar terms and incorporated them into the Taichu calendar. He stipulated that even solar terms such as rain, spring equinox and grain rain must appear in the current month, otherwise this month should be set as the leap month of last month. This leap principle has been used until now. (Xinhua News Agency)