First of all, the latest data of the length of the tropic year is given. Liu Hong found that the tropical year in the previous calendar was too long. In the dry calendar, he set a new value of 365.2468 days, which is more accurate. This new tropical year length value has ended the long-term wandering or even retrogression of the determination accuracy of tropical year length, and opened up a correct direction for future generations to study this value.
Secondly, great progress has been made in the study of lunar motion, and a unique quantitative description method has been given. Liu Hong affirmed the predecessors' understanding of the moon's motion inhomogeneity, and on the basis of recalculation, for the first time, it was clearly determined that the value of the moon passing through perigee twice was 27.5534 days. Liu Hong pioneered a digital table to correct and calculate the uneven motion of the moon, that is, the digital table of the difference between the actual latitude and the average latitude of the moon every other day after the perigee. It provides a practical method for calculating the real mobility of the moon and lays a foundation for the traditional calculation method of this topic in ancient China. Liu Hong pointed out that the moon runs along its own unique orbit, and the included angle between the ecliptic and the ecliptic is about 6 degrees. This is close to the measurement results obtained today. He also made a digital table of degrees inside and outside the ecliptic, from which the degrees of the moon from the north and south of the ecliptic at any time can be calculated. Liu Hong expounded the new astronomical concept that the intersection of the ecliptic and the ecliptic recedes from east to west in the stellar background, and determined the specific degree of daily retreat of the intersection of the ecliptic and the ecliptic.
Thirdly, a new mating cycle value is proposed. Liu Hong proposed that the length of an annual solar eclipse is 346.6438+055438+0 days. This value is more accurate than that obtained by his predecessors and contemporaries, and its accuracy is second to none in the world at that time. Liu Hong also put forward the concept of eclipse limit, pointing out that only when the distance between the sun and the intersection of yellow and white is less than 14.33 degrees, an eclipse or a lunar eclipse may occur, which is called eclipse limit, and it is a clear and concrete numerical limit to judge whether an eclipse occurs. Liu Hong created a method to calculate the distance between the moon and the intersection of yellow and white and the position of the sun. In fact, this has solved the problem of calculating the size of the solar eclipse and the starting position of the solar eclipse deficit, but it is not elaborated in the Dry Image Calendar.
The fourth is the contribution to the calculation and compilation of astronomical data tables. Together with Cai Yong, a writer and calligrapher in the late Eastern Han Dynasty, Liu Hong completed the calculation and compilation of astronomical data tables such as the sun, ecliptic, shadow length, day and night length and dark stars in the 24 solar terms. This table was recorded in the calendar of the Eastern Han Dynasty, and later became one of the traditional contents of the ancient calendar of China.
Liu Hong put forward a series of new astronomical data, new tables, new concepts and new calculation methods, which pushed the study of ancient sun, moon movement and solar eclipse in China to a new stage. His Dry Elephant Calendar is a milestone in the maturity of the ancient calendar system in China.