Every now and then a dark spot glides across our Sun. This rare moment hits when the planet Venus slides in between the Sun and Earth, obscuring a small portion of the sun.

During a transit, Venus can sneak as close as 38 million kilometres to our home planet. The transit usually lasts about six hours and happens in pairs that eight years apart, each pair is separated by around 120 years.

On 6 June 2012 Venus transited the Sun, this is the second transit of the set – the first scrolled past in 2004. So, for those who missed it, they’ll have to wait until 2117 for the next one. (Sorry!)

This transit wasn’t just beautiful, it will also help scientists better understand Venus and even help find exoplanets.

While Venus, named after the Roman goddess of love, might look enticing from Earth – if you took a sojourn to this planet you would either be burned alive by the 464 degree C temperatures, or crushed to death by the overpowering atmospheric pressure. And although we know some stuff about this planet, there are still a great many unknowns.

For example, the clouds of Venus completely swirl around the planet in four days – and scientists don’t really know how winds could rotate so quickly.

How will the Transit help us know more about Venus?

As Venus’ first makes contact with the edge of the Sun’s disk, it becomes outlined by a thin arc of light, called the aureole. This mysterious arc is caused by light waves writhing through Venus’ atmosphere.

The brightness and thickness of the aureole depends on the height of the atmospheric layers above Venus’s cloud tops, and the density and temperature of Venus’ atmosphere.

Measuring the density of Venus’ atmosphere has proved incredibly difficult because it changes so much. But, during the transit, scientists will be able to use a variety of tools to record Venus’ atmosphere – and from this, they can understand the temperature, density and other characteristics of Venus’ clouds.
Astronomers will also use the transit of Venus to better understand the characteristics of exoplanets, which are planets outside our Solar System.

How? NASA’s Kepler spacecraft – launched in 2009 – hunts exoplanets. It does this by constantly monitoring the brightness of 150,000 stars found between 600 and 3,000 light years from Earth. If the brightness of a star regularly dims, it suggests a circling planet might be causing the change. For example, the transit of Venus will dim the Sun’s light by just a tenth of one per cent. The amount of light dimmed also gives information about the planets’ masses.

Measuring the rate that the Sun dims, or the Moon dims, when Venus is transiting will let scientists confirm and bolster calculations to allow Kepler to detect new planets.

For more information watch ABC’s Catalyst.