Solar eclipses, particularly of the total or near-total kind, are among the most dramatic and memorable of all astronomical events. But what causes these striking phenomena in the first place, and why do they occur at certain times and not others?
Eclipses occur due to the alignment of three different celestial bodies: the Earth, Moon and Sun. Without going into too much astronomical detail, you can picture the Moon as revolving around the Earth in a roughly circular orbit, while both bodies are illuminated by the much more distant Sun. The Moon takes about a month to complete a single orbit, during which time there are two occasions when the Sun, Moon and Earth lie along an approximately straight line. When it happens in that order, and the Moon looks very close to the Sun in Earth’s sky, we call it a ‘new Moon’; when it’s in the order Sun-Earth-Moon, we call it a ‘full Moon’, because the Moon’s disc is fully illuminated by sunlight when viewed from Earth.
Most months, this alignment isn’t perfect because the Moon orbits Earth in a slightly different plane from the orbit of the Earth-Moon system around the Sun. For example, a new Moon usually appears slightly offset from the Sun in the sky, rather than bang on top of it. But occasionally, the three bodies really
