The recent annular eclipse isn't the only event that will hide some of the Sun this year. Tuesday, June 5, the Earth will be treated to an event that will obscure far less of the Sun, but is more significant both scientifically and due to its rarity: the transit of Venus. For a short period of time tomorrow, Venus' orbit will take it in between the Sun and Earth, casting a small shadow across the surface of the Earth. Prime viewing areas will be in North America, Europe, and parts of Africa and Asia. If this is your sort of thing, it's not to be missed, because the next chance to see a transit won't come around until 2117.

NASA has set up a webpage with details on the transit, and will be webcasting the event if you can't make it to somewhere where it's visible. If a live viewing is an option, you can find a map of local options that can help you find a place to go. As always, directly viewing the sun for any length of time should be approached with caution and done with appropriate equipment.

Past transits of Venus have had some scientific significance from very early on, since they helped astronomers refine orbital models of the Solar System and start calculating the distances between different objects within it. This year's version, however, has taken on new significance due to our recent success in identifying exoplanets.

With the huge collection of exoplanet candidates spotted by the Kepler telescope and other methods, researchers are now considering how to move on to the next step: examining whether we can successfully extract information about an exoplanet's environment using the small fraction of light from distant stars that passes through its atmosphere as the planet orbits in front of its host star. In this case, we'll be able to watch up close with a variety of instruments and analyze what we see using a large amount of knowledge about the composition of Venus' atmosphere. In addition, the ESA has a mission, Venus Express, that will provide information on the planet's atmosphere as the transit takes place.

The transit will also help researchers who are studying the Sun. Due to the detail with which we understand Venus' orbit, we actually know precisely where it will cross the Sun. The Solar Dynamics Observatory will use this to establish an exact location for the Solar North Pole, which will help us interpret further measurements. The contrast between the shadow of Venus and the nearby Sun will also help calibrate some of the instruments on board this observatory. The SDO will attempt to image the atmosphere of Venus in the UV range, which can be used to search for traces of oxygen.

All of this should provide us with an exceptional perspective on what we can detect from nearby planets, which we can then use to design hardware and techniques that should allow us to have a chance of gathering similar information from distant worlds. (We'll have more information on this as our coverage of the World Science Festival continues.)