Eclipses happen on Earth because of an amazing coincidence. Calculate, using the information inside the front cover, the angular diameter (in radians) of the Sun and the angular diameter of the Moon, as seen on Earth. The angle in radians is equal to the arc length, divided by the radius. The arc length would be the diameter of the sun or the moon, and the radius would be their distance from us:
Moon:
radius = 1.74x103km, diameter = 3.48x103km
distance from us = 384x103km
Subtended angle:
q = s/r = (3.48x103km)/(384x103km) = 0.0090625
Sun:
radius = 6.96x105km, diameter = 1.392x106km
distance from us = 149.6x106km
q = s/r = (1.392x106km)/(149.6x106km) = 0.009304813
so 0.0090625 is almost equal to 0.009304813
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