Occultations

There will be four other occultations in 2020, all visible from the Southern Hemisphere.

All values of ΔT before 1955 depend on observations of the Moon, either via eclipses or occultations.

It is only when Saturn lies near the point that the moon’s orbit crosses the “plane of the ecliptic” that occultations can happen – and then they occur every time the moon swings by, until Saturn moves away from the crossing point.

Occultations in which the larger body is neither the Sun nor the Moon are very rare.

Once every 42 years, when Uranus has an equinox and its equatorial plane intersects the Earth, mutual occultations of Uranus's moons become possible.

Radio occultations by the planet resulted in better measurements of Jupiter's diameter and the amount of polar flattening.

Rømer observed immersions in C from the symmetric positions F and G, to avoid confusing eclipses (Io shadowed by Jupiter from C to D) and occultations (Io hidden behind Jupiter at various angles).

Rømer's observations of the occultations of Io from Earth The first quantitative estimate of the speed of light was made in 1676 by Rømer (see Rømer's determination of the speed of light ).