Exploring the discovery of exoplanets made from transit observations.
A transit occurs when one smaller object directly passes in front of a star, as seen from the vantage point of the observer. As the object moves across the disk, a small amount of starlight is blocked. The periodically occurring brightness reduction of the host star is observable which allows for exoplanets --planets orbiting stars other than the Sun-- being discovered. Since the invention of the telescope, Venus has been observed to transit the Sun seven times, in 1639, 1761, 1769, 1874, 1882, 2004 and 2012.
The next times will only be in 2117 and 2125.
When a smaller star partially blocks a larger star, a primary eclipse occurs. A secondary eclipse occurs when the smaller star is occulted, or completely blocked, by the larger star.
A transit of Venus across the Sun takes place when Venus passes directly between the Sun and Earth. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun.