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. ...

... The greater the distance, the smaller the parallax. ... That triangle has the same proportions as the much larger triangle ABC, and therefore, if the distance B'C to the thumb is 10 times the distance A'B' between the eyes, the distance AC to the far landmark is also 10 times the distance AB. ... The most distant objects our eyes can see are the stars, and they are very far indeed: light which moves at 300,000 kilometers (186,000 miles) per second, would take years, often many years, to reach them. ...

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. ...