For the first time, astronomers have glimpsed one of Uranus's 27 moons passing in front of one of its siblings – a fleeting alignment that can reveal information about the moons, such as their mass, that cannot be gleaned in any other way. Researchers hope this will be the first in a bonanza of data returned from Uranus in the next year. That is because Uranus, which orbits the Sun every 84 years, is in an ideal geometry to view its moons. Such periods come around only once every 42 years, and the next will not occur until 2049.This series...