Eclipses and occultations happen when three bodies all lie on a straight line, so that the light from one of them is prevented from reaching another.
Eclipses of the Sun happen when the Earth, Moon and Sun line up so the Moon is between the Sun and the viewer. Total eclipses only affect a narrow belt.
Eclipses of the Moon may be seen from half of the Earth. They happen when the Earth moves between the Sun and the Moon so as to entirely shade it.
The fact that we can observe a solar eclipse proves that the Moon is closer to the Earth than the Sun, and this was known by the ancient Greeks.
In a lunar eclipse, the surface of the Moon appears red because some of the Sun's light is refracted by the Earth's atmosphere, which filters out blue light.
When scientists in the Mediterranean saw eclipses of the Moon, these showed them that Earth was a sphere, based on its shadow.
Further evidence of a spherical Earth in lunar eclipses came when scientists compared the time of night when eclipses were seen in different longitudes.
Solar eclipses also showed Greek astronomers that the Sun was further from the Earth than the Moon was.
When the moons of Jupiter are eclipsed by Jupiter, this happens at intervals which can be predicted. Navigators could use this to find longitude.