Planetary Transits is an interactive educational program designed to teach students about the movements of the planets in our solar system. Through a series of interactive activities, students will learn about the orbits of the planets, the effects of gravity, and the effects of planetary transits on the Earth. The
From Wikipedia
In astronomy, planetary transits and occultations occur when a planet passes in front of another object, as seen by an observer. The occulted object may be a distant star, but in rare cases it may be another planet, in which case the event is called a mutual planetary occultation or mutual planetary transit, depending on the relative apparent diameters of the objects.