occultation

The hiding of one celestial body behind another — a star disappearing behind the moon, a moon slipping behind a planet. An eclipse is a special case of occultation, but the word applies more broadly: any time one object in the sky passes in front of another, blocking it from view. Occultations are instantaneous — a star winks out in a fraction of a second as the moon’s limb crosses it — and astronomers use the precise timing to measure the positions and sizes of objects with extraordinary accuracy.