This section describes the calculation by which Aristarchus used the duration of a total lunar eclipse to deduce the distance of the Moon. ... This lesson plan supplements: "How Distant is the Moon--1", section #8c: on disk Shipprc2.htm , on the web . ... The shadow of the Earth at the Moon's distance is narrower than the Earth, because the Sun is seen not as a point but as a disk 0.5 degrees wide. ... An eclipse of the Moon is the passage of the Moon through the shadow of the Earth. ...