The front of the Beijing Winter Olympics gold medal (left) and the back, issued by Xinhua News Agency (photo courtesy of the Beijing Winter Olympics Organizing Committee)
As the pace of the Beijing Winter Olympics is getting closer, the medal design of this Winter Olympics and Paralympics also attracted the attention of many people.
According to the design team, the pattern on the front of the medal is derived from the traditional string pattern jade, while the concentric rings and 24 dots inlaid on the back are inspired by ancient astronomical maps, symbolizing the vast starry sky and the Winter Olympic athletes like stars Bright.
So, which ancient astronomical picture 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 for the medal came from the "Seven Hengs Six Diagrams" in "Zhou Pi Suan Jing". The relationship between.
Different from the five circles on the medal, there are seven equally spaced concentric circles on the "Seven Balances and Six Divisions Diagram". Each circle is a "balance". Indicates the orbit of the sun at different times in a year.
On the Qiheng map, the outermost circle with the largest radius is the outer scale. At this time, the sun's orbit is the farthest from the observation point, indicating the winter solstice and the weather is cold.
The innermost circle with the smallest radius is the internal balance. At this time, the sun's orbit is closest to the observation point, indicating the summer solstice and the weather is hotter.
From the winter solstice to the summer solstice, the five levels in the middle represent the solar orbit circles of the five solar terms: Great Cold, Rain, Vernal Equinox, Guyu, and Xiaoman.
From the summer solstice to the winter solstice, the 5 levels in the middle represent the solar orbit circles of the great heat, the little heat, the autumnal equinox, the frost, and the light snow respectively.
From the external scale to the internal scale, and then from the internal scale back to the external scale, the two stages are divided into 12 equal parts, and the total is twenty-four solar terms.
You might be thinking, is the Qiheng map a "crude" division of the sun based on temperature differences only when the ancients lacked modern astronomy knowledge?
The answer is not so.
The reason is that the Qiheng map is not a plane concentric circle, but a coaxial circle parallel to the sphere. This axis runs through the north celestial pole, which is the axis of the earth's rotation.
When the ancients constructed their outlook on the universe, they did not know that the day and night changes and the changes in the four seasons were caused by the rotation and revolution of the earth.
They imagined a celestial sphere that is concentric and coaxial with the earth and has an infinite radius.
The sun, moon and stars are all located on the sphere, rotating from east to west with the center of the north celestial pole.
It can be seen that the seven balances diagram does not divide the daily heights mechanically on the plane, but depicts the trajectory of the sun moving between different balances along the spherical surface during the year.
At the same time, in the visual motion, the sun still rotates around the polar axis once a day, so there is the difference of day and night.
If the apparent path of the sun moving between different scales in a year is connected, the "ecliptic" of the sun's rotation on the celestial sphere is formed.
The West divides the stars of the zodiac into twelve constellations, and in ancient China it was named twenty-eight constellations.
They circle the North Star, rising and falling in the west day after day.
The ecliptic is divided into 24 equal parts, and each arc of the sun is divided into one quarter.
Because the sun does not move at a uniform speed, the span of each solar term is not necessarily equal.
At the same time, there is a corresponding relationship between the "seven balances and six divisions" and the five zones on the earth. The middle balance corresponds to the equator, and the inner balance and the outer balance correspond to the Tropic of Cancer and the Tropic of Capricorn, respectively.
Twenty-four solar terms is a major creation in the field of ancient agronomy in our country. For thousands of years, it has played an important role in indicating phenological seasons and guiding agricultural production.
The Western Han astronomer Luo Xiahong determined the date of the twenty-four solar terms and compiled it into the "Taichu Calendar".
He stipulated that even-numbered solar terms such as rain, vernal equinox, and valley rain must appear in the current month, otherwise this month must be the leap month of the previous month. This principle of intercalation has been used today.
◎Liu Huizhong