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古代以已知的地球半径R为基础,测量地月距D_M、地日距D_S和月半径R_M、日半径R_S,方法如下( 改用现在的数据)。第一步:求地日距D_S与地月距D_M,之比。正当月面的一半明亮时,∠M=90°。从地球测得∠α=89°51'12"。所以 D_S=1/(cos89°51'12")D_M=391D_M。第二步:求日半径 R_S与月半径R_M之比。
In ancient times, based on the known radius R of the Earth, the monthly distance to ground D_M, the ground-to-ground distance D_S, the monthly radius R_M, and the daily radius R_S are measured. The method is as follows (use current data). The first step is to find the ratio of ground-to-ground distance D_S to ground-month distance D_M. When half of the lunar surface is bright, ∠M=90°. From the Earth, we measured ∠α=89°51’12“, so D_S=1/(cos89°51’12”)D_M=391D_M. Step 2: Find the ratio of daily radius R_S to monthly radius R_M.