Senin, 30 April 2012

Watch the skies! Once-in-a-lifetime event as Venus passes in front of the sun

Watch the skies! Once-in-a-lifetime event as Venus passes in front of the sun

  • Rare phenomenon will not be seen again for more than a century
  • Venus will be visible as a black dot in front of the sun for five or six hours
  • 'Transits' used to calculate distance from Earth to the Sun in 1769

By Rob Waugh

PUBLISHED: 20:24 EST, 30 April 2012 | UPDATED: 20:24 EST, 30 April 2012

Venus will be visible as a blot against the Sun in June in a rare 'transit' in front of the star - the phenomenon is so uncommon that the next one will be in 2117.

The transits of Venus in front of the sun to calculate the distance from Earth to the sun in 1769 - using a method proposed by astronomer Edmond Halley, after whom the comet is named.

On 5 and 6 June, Venus will appear as a small black dot on the Sun's surface in a rare transit, taking six hours to complete its journey.

Venus transits in front of the sun in 2004: The orbits of the two planets are angled oddly, so the next transit won't be until 2117

Venus transits in front of the sun in 2004: The orbits of the two planets are angled oddly, so the next transit won't be until 2117

HOW VENUS HELPED US CALCULATE THE DISTANCE FROM THE EARTH TO THE SUN

Transits of Venus occur only on the very rare occasions when Venus and the Earth are in a line with the Sun. At other times Venus passes below or above the Sun because the two orbits are at a slight angle to each other.

Transits occur in pairs separated by eight years, with the gap between pairs of transits alternating between 105.5 and 121.5 years â€" the last transit was in 2004.

In 1716, Edmond Halley proposed using a transit of Venus to predict the precise distance between the Earth and the Sun, known as the astronomical unit. 

As a result, hundreds of expeditions were sent all over the world to observe the 1761 and 1769 transits. A young James Cook took the Endeavour to the island of Tahiti, where he successfully observed the transit at a site that is still called Point Venus.
 

Transits of Venus only occur when Venus and the Earth are in line with the Sun, as normally it passes below or above the Sun because the two orbits are at a slight angle to each other, reports journal Physics World.

The journey usually occurs in pairs separated by eight years, with the gap between pairs of transits alternating between 105.5 and 121.5 years. The last transit happened in 2004.

Massachusetts scientists are hoping the transit will confirm their theory about a phenomenon called 'the black-drop effect' - a strange, dark band linking Venus's silhouette with the sky outside the Sun that appears for about a minute, starting just as Venus first enters the solar disk.

They will concentrate on observing Venus's atmosphere as it appears when the planet is only half on to the solar disk, believing observations will help astronomers who are looking for extrasolar planets orbiting stars other than the Sun.

Jay Pasachoff, an astronomer at Williams College, Massachusetts, said: ‘Doing so verifies that the techniques for studying events on and around other stars hold true in our own backyard.

In 1769, teams of astronomers around the world used the transit of Venus to calculate the distance from the Earth to the Sun

In 1769, teams of astronomers around the world used the transit of Venus to calculate the distance from the Earth to the Sun


‘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.

'We are fortunate in that we are truly living in a golden period of planetary transits and it is one of which I hope astronomers can take full advantage.’

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