On the reverse side of the Moon, just south of the Sea of Moscow, is a crater named Tsu Ch’ung-Chih. Who is Tsu Ch’ung-Chih? What did he do to be thus admitted to the honoured company of Maxwell and Hertz, of Mendele’ev and the Curies, of Lomonosov and Tsiolkovsky?

Tsu Ch'ung-Chih was a Chinese mathematician-astronomer who nourished in the fifth century A.D. He made notable contributions to the calendar calculation and determined several constants with remarkable accuracy. For example, he gave a value of 27·21223 days for the length of the nodical month, the modern value being 27·21222 days. As another example, he found that the planet Jupiter completes seven and one-twelfth circuits of the heavens in every seven cycles of 12 years; this corresponds to a sidereal period of Jupiter of 11-859 years, which differs from the modern value by only 1 part in 4000.