Transit of Venus
Transit of inferior planets
Mercury and Venus are inferior planets in the Solar System as they are nearer to the Sun than the Earth.
A transit of an inferior planet occurs when the inferior planet, the Sun and the Earth align in a straight line with the inferior planet in between. During the transit, the inferior planet appears as a dark dot across the Sun's disc. This phenomenon does not occur every year because of the inclination of the inferior planet's orbit to that of the Earth (Figure 1).
Figure 1 The relative positions of the Sun, an inferior planet and the Earth during the transit of the inferior planet.
Transit of Venus
Venus is the second closest planet to the Sun in the Solar System. It is also closer to the Earth than any other planets. Besides the Sun and the Moon, Venus is the brightest object in the sky.
Transit of Venus is a rare astronomical phenomenon. The next transit will occur on 6 June 2012. After which it will only recur in 2117.
The different stages during the transit of Venus on 6 June 2012
Beginning of transit:
Exterior contact: Venus begins to enter the Sun's disc
Interior contact: Venus is just entirely inside the Sun's disc
End of transit:
Interior contact: Venus begins to leave the Sun's disc
Exterior contact: Venus is just entirely outside the Sun's disc