The Transit of Venus across the Sun is one of the rarest cosmological events you'll ever see. In early June, Venus will pass between the Earth and the Sun for the last time for more than 105 years: the next transit will not happen until 2117. The last transit occurred in 2004 — the first time that the event could be seen using modern space telescopes. Scientists hope the 2012 transit will give them more clues about the atmosphere of Venus and planets in other solar systems. The timing of the movement was critical to astronomers during the 18th and 19th centuries, as it provided a way to measure the distance between the Earth and the Sun. This measurement, known as the astronomical unit, allowed them to work out the scale of our solar system and the distances of each of the planets circling the sun.

In our part of the world, the transit will be visible at dawn from sunrise on 6 June, but it should not be observed without appropriate eye protection.

For more information go to www.abc.net.au/science/articles.