Educator's Guide to Eclipses . ... In a solar eclipse you observe the Sun (using only safe methods, of course). ... In a lunar eclipse you observe the Moon. ... Because of the geometry described below, you can only view a solar eclipse when the Sun is up, and the Moon is nowhere to be seen. ... Eclipses occur when the Sun, Earth and Moon line up. ... In a solar eclipse the Moon passes directly in front of the Sun. ... In a lunar eclipse the Moon moves into Earth's shadow. ...

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. ...