When do transits of Venus happen?
Orbit-The path taken by a planet around the Sun.
Transit-The movement of a planet across the face of the Sun as viewed from Earth. The dark spot of the planet is much smaller than the disk of the Sun.
Eclipse-The blockage of sunlight shining on one planet due to a second planet or moon located temporarily between them. For a solar eclipse, the moon is between Sun and Earth and its black disk matched the size of the Sun almost exactly, unlike a transit where the black disk is much smaller than the Sun.
Synodic Period-The time interval between planetary conjunctions with the Sun when the same pattern is repeated as viewed from Earth.
Conjunction-When a planet is closest to the Sun as viewed from Earth.
Conjecture-An idea which seems reasonable but has not been mathematically or scientifically proven.