Why Do Eclipses Occur?

Part of the Astronomers' Observing Guides book series (OBSERVING)

We live on a planet that, for its size, has an unusually large Moon. Indeed, before the discovery of Pluto’s Moon, Charon, in 1978, the relative size of our satellite was unique in the solar system. Moving outwards from the Sun and therefore dealing with the terrestrial planets first: Mercury and Venus have no moons, Earth has one, Mars has two tiny moons and then we arrive at the asteroid belt. On the other side of this swarm of hundreds of thousands of minor planets we encounter the four gas giants. Jupiter has three moons that are larger than our own, namely Io, Ganymede and Callisto; Europa is only slightly smaller, but they are dwarfed by the 140,000 km diameter parent planet. Saturn has an incredible 30 moons, but Titan, the only moon in our solar system with an atmosphere, is the only one larger than Earth’s Moon. An image of Saturn itself, eclipsing the Sun with ease, is shown in Fig. 1.1. None of the 20 satellites of Uranus come anywhere near the size of our Moon and distant Neptune’s large satellite Triton is only three-quarters our own Moon’s diameter. It is really astonishing that the Earth has such a relatively large satellite (Table 1.1).


Solar Eclipse Atomic Clock Lunar Orbit Moon System Total Solar Eclipse 
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© Springer Science+Business Media, LLC 2007

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