May 1, 2012
Rare Transit Of Venus Event Expected In June
A once-in-a-lifetime event is on its way -- an event that hasn´t occurred since 1882 and will not occur again until 2117 -- and will be a spectacular event for millions of people all around the world.
The Transit of Venus, as it is called, occurs when the planet passes across the face of the Sun. It is viewable from Earth as a small black dot on the solar surface and takes about six hours to complete its transit. The event will occur on June 5 and 6 and will be visible across much of the world.
Transits of Venus only occur when the Earth and Venus are in line with the Sun, according to Jay M Pasachoff, an astronomer at Williams College, Massachusetts. Normally Venus passes below or above the Sun because our orbits are slightly angled to one another, he said, reporting in the journal Physics World.
Transits occur in pairs separated by eight years, with the gap between pairs of transits alternating between 105.5 and 121.5 years -- Venus´s last transit was in 2004.
Transits were first theorized by Renaissance astronomer Nicolaus Copernicus in 1543, and scientists later were able to predict and record the transits of both Mercury and Venus based on Copernicus´s theories. Johannes Kepler successfully predicted both planets would transit the Sun in 1631. However, the first transit of Venus to be viewed didn´t occur until 8 years later, in 1639.
The 1639 event was only seen, however, by two people: Jeremiah Horrocks, an English astronomer from Much Hoole, Lancashire, and his correspondent, William Crabtree, from Manchester.
Edmond Halley in 1716 theorized that the transit of Venus could give a precise distance between the Earth and the Sun, known as an astronomical unit (AU). During the next Transits of Venus, in 1761 and 1769, hundreds of expeditions were sent out all over the world to observe the events.
Pasachoff and colleagues are hoping to confirm a theory about a phenomenon they call “the black-drop effect” -- a strange, dark band lining Venus´s silhouette with the sky outside the Sun that only appears for about a minute as Venus begins its transit of the Sun.
By concentrating on observing Venus´s atmosphere as it appears when it is only half onto the solar disk, Pasachoff said they should be able to confirm their theory. He also believes observations of the transit will help astronomers who are looking for extra solar planets orbiting other stars.
“Doing so verifies that the techniques for studying events on and around other stars hold true in our own backyard,” wrote Pasachoff. “In other words, by looking up close at transits in our solar system, we may be able to see subtle effects that can help exoplanet hunters explain what they are seeing when they view distant suns.”
French astronomers are taking a slightly different approach to the transit of Venus. They will be using the Hubble Space Telescope to observe the effect Venus´s transit will have on the Moon, expecting the transit will slightly darken our lunar neighbor.
And forget about watching the transit of Venus from Earth. Pasachoff said they are hoping to use Hubble to view a transit of Venus from Jupiter, which will occur on September 20.
Then on December 21, the team plans to use NASA´s Cassini spacecraft to view the transit of Venus as seen from Saturn.