Warum der Mond relativ so groß wie die Sonne ist

Der Mond und die Sonne sind von der Erde aus gesehen genau gleich groß, was bei Sonnenfinsternissen im Diamantring-Effekt führt. (Der Mond ist übrigens nicht überall auf der Erde genauso groß, wie die Sonne, wie man auf diesem Bild einer Sonnenfinsternis sehen kann.) New Scientist hat jetzt jedenfalls ein Special über das „Unknown Solar-System“, darunter behandeln sie genau diese Frage: Warum ist der Mond relativ genauso groß, wie die Sonne?

It is all thanks to a striking coincidence. The sun is about 400 times as wide as the moon, but it is also 400 times further away. The two therefore look the same size in the sky - a unique situation among our solar system's eight planets and 166 known moons. Earth is also the only planet to harbour life.


As Earth spins on its own axis, it has a natural tendency to wobble, owing to the varying pull on it from other bodies such as the sun. The unseen hand of the moon's gravity gently damps that wobble, preventing rotational instabilities which would otherwise have caused dramatic changes in Earth's climatic zones over time. Such instabilities would have made it much more tricky for life to get started on our planet.

Earth's position in the "habitable zone" around the sun where liquid water is abundant is undoubtedly the single most important factor in its fecundity. But the presence of a large moon - one large enough to cause total eclipses - might also have been crucial. If so, that has important consequences for the search for life on other planets.

Our Unknown Solar System (via Digg)