

The position of the Sun, Moon, and Earth during a lunar eclipse is shown in the given figure.
Distance of the Moon from the Earth = 3.84 × 108 m
Distance of the Sun from the Earth = 1.496 × 1011 m
Diameter of the Sun = 1.39 × 109 m
It can be observed that ΔTRS and ΔTPQ are similar. Hence, it can be written as:
PQ / RS = VT / UT
1.39 x 109 / RS = 1.496 × 1011 / 3.84 × 108
RS = (1.39 × 3.84 / 1.496) × 106 = 3.57 × 106 m
Hence, the diameter of the Moon is 3.57 × 106 m.
