Mercury Transit, May 2016

Although Mercury zooms around the sun every 88 days, Earth, the sun and Mercury rarely align. And because Mercury orbits in a plane that is tilted from Earth’s orbit, it usually moves above or below our line of sight to the sun.

Transits provide a great opportunity to study the way planets and stars move in space—information that has been used throughout the ages to better understand the solar system and which still helps scientists today calibrate their instruments.