Chapter 49 The second period of rendezvous

The various visual phenomena of planets will repeat once in a while, which is called one-time or one-time sight, which is the rendezvous period in modern astronomy.The ancients have long noticed that this law is related to the relative positions of the planets and the sun.Before the Dayan Calendar of the Tang Dynasty, the rendezvous cycle was defined as the time interval between seeing the next morning at the beginning of the morning, but the concept of "seeing at the beginning of the morning" was very inaccurate.It literally means first seen in the morning, and refers to the shortest distance from the sun when a planet located to the west of the sun can be distinguished by the naked eye when it is first seen. "See you in the morning" will of course vary from person to person, and it is an unreliable judgment.Therefore, starting from the Dayan calendar, the definition of the conjunction period is changed to: the time interval between two consecutive conjunctions with the sun.Exactly the same as the modern definition.

It can be seen from the table below that during the Spring and Autumn Period and the Warring States Period, people had mastered the rendezvous periods of Venus, Jupiter and Mercury. Mercury was too close to the sun to be observed, so the data error of Mercury was too large.In the Western Han Silk Book "Five Stars" unearthed at Mawangdui, Changsha, the period values ​​of Venus, Jupiter and Saturn are recorded relatively accurately, and the error of Venus is within half a day.In Zu Chongzhi's Great Ming calendar in the Northern and Southern Dynasties, the errors of the five major planetary rendezvous periods are all less than 0.0022 days.Less than 100 years later, the great career calendar of the Sui Dynasty showed higher observation capabilities. Except for Mars, which had an error of 1% day, the rest of the planets were all below 2‰ days, that is, less than 2′53″. After the great career calendar, The cycle values ​​of planetary conjunctions have remained at such a high level throughout the ages.