Also, during the transit of 1761 astronomers noticed a halo of light around the planet’s dark edge, revealing Venus to have an atmosphere.
As a planet passes in front of a star, it temporarily blocks out a tiny portion of the starlight, revealing its presence and providing information about the planet’s size. Europe’s CoRot space telescope has used this technique to discover over 20 exoplanets.
Transits are also being used to search for exoplanets that may harbor life. If the planet has an atmosphere a small fraction of the light from the star will pass through this atmosphere and reveal its properties, such as the presence of water or methane.
The 2012 transit will be visible in its entirety only from the western Pacific, eastern Asia, eastern Australia and high northern latitudes.
For the India, the transit will begin in the around 3:39am on 6 June.