[填空题]
Eclipses happen on Earth because of an amazing coincidence. Calcux m mxah/ e8r5,:cx,lslate, /cmft7)e7kthovy*5d using the dcto/ thy7e*m7f)kv5information inside the Front Cover, the angular diameters (in radians) of the Sun and the Moon, as seen on Earth. Sun = $rad$ Moon = $rad$