- noun a situation when the Moon passes between the Sun and the earth or when the Earth passes between the Sun and the Moon, in both cases cutting off the light visible from Earth.
- The cutting off of the illumination of an astronomical object, as in an eclipse of the Moon, when the Earth comes between the Moon and Sun, so that its shadow crosses the Moon’s surface. The term is also used universally but in fact wrongly for occasions when the Sun’s disc is blotted out by the Moon from the point of view of Earthly observers. These events are in fact occultations of the Moon, or eclipses of the Earth. The Moon and the Sun are almost exactly the same size – about half a degree – in the Earth’s sky, making it possible, by coincidence, to observe the eclipsed Sun. This provides a powerful experimental tool for examining the Sun’s atmosphere. The Moon’s shadow at the Earth is so narrow that any given solar eclipse is visible only from a narrow line on the Earth’s surface. If the Moon is too far away in its orbit the full eclipse effect is not seen, but an annular eclipse is observed instead.
Origin & History of “eclipse”
From the point of view of the observer, an object which has been eclipsed has ‘gone away’ – is no longer there. And that in fact is the etymological foundation of the word. It comes, via Old French and Latin, from Greek ékleipsis, a derivative of ekleípein ‘no longer appear or be present’. this was a compound verb formed from the prefix ek- ‘out, away’ and leípein ‘leave’ (a distant relative of English leave). Its adjectival derivative, ekleiptikós, passed into English as ecliptic (14th c.), which was applied to the apparent path of the Sun relative to the stars because that is the line along which eclipses caused by the moon occur.