Nathan Sivin, a professor at the University of Pennsylvania in the United States, looked into China's Season-granting calendar (Shoushi Li) reform of 1280, which took place in early years of the Yuan Dynasty (1271-1368) established by China's Mongol rulers.

In the mid 13th century, the then calendar Great Enlightenment system (Daming Li) was woefully inaccurate.

Yet according to Sivin, the idea to reform the calendar was not spawned from this inefficient time keeping.

For the Mongols, technical skill implied spiritual superiority. As rulers, they strove to "mobilize and monopolize the spiritual forces of the realm" to throw more weight behind their rule in China.

As early as 1251, Liu Bingzhong (1216-1274), senior consultant to the emperor Khublai Khan (1215-1294), suggested reforming the calendar as a way of legitimizing imperial Mongol authority.

In order to revise the Daming Li, Khublai Khan brought together not only Chinese astronomers but also Muslim scholars from Arabia and Persia, areas also occupied by the Mongols at the time. They wanted a second opinion on the reading of heavenly signs and portents.

Although Islamic astronomers such as Persian scholar Jamal al-Din (1267-1291) had by that time started using sophisticated observation and computing techniques and equipment, those who did the lion's share of the planning and running of the project were Chinese.

Some of the Chinese scholars taking part in the program were not only astronomers but also scholars of Confucianism, which dominated Chinese intellectual thought at the time. Only they knew how to effectively interpret the new calendar to the intellectuals.

With the efforts of the Chinese and Islamic scholars, and with huge investment from the government, the Season-granting calendar was successfully established, which remained, with a little adjustment, the main calendar in China until the Western system arrived in the late 19th century.

The reforming of the calendar was considered a dialogue between humankind and heaven in ancient China.

It was not a singular event, however. Other natural sciences also had political and ethical significance in the country at the time, according to Sun Xiaochun, a history of science professor at the Chinese Academy of Sciences.

In his thesis, Sun points out that in ancient China the legitimacy of rulers, their method of rule and the self-evaluation and self-adjustment of that governance all originated from nature.

"For example, a Chinese calendar was not just an arrangement of days, months and years in numbered sequences, but also a complete mathematical technique for calculating the ephemeris of the sun, moon and planets," Sun said.

Based on such an understanding of nature, laws like those protecting seedlings or animal cubs were laid down in ancient China.

"Do not kill cubs because this will destroy the natural harmony," it is often said in ancient Chinese technical books.

(China Daily August 3, 2005)