Venus to take rare voyage across the Sun

A picture taken 08 June 2004 shows the planet Venus transiting in front of the sun. The last visible transit of Venus occurred 06 December 1882 and the next one will be in 2012. (AFP Photo / Attila Kisbenedek)
Venus is set to pass directly between Earth and the Sun in one of the rarest celestial phenomena that can be seen from our planet. Scientific experiments are planned during the transit, some of which could help the search for life on other planets.

The event has only been recorded eight times in history and the next occurrence is predicted to happen in 2117. Transits of Venus happen in pairs eight years apart, with more than a century between cycles.

Tuesday’s display will kick off at 22:09 GMT and is set to last for six hours and forty minutes.

Scientists say the celestial show will be visible to stargazers in all continents and advise observers to only use telescopes fitted with solar filters to protect their eyes.

"The timing favors observers in the mid-Pacific where the sun is high overhead during the crossing," NASA Science's Tony Phillips wrote in a blog post. "In the USA, the transit will be at its best around sunset. That's good, too. Creative photographers will have a field day imaging the swollen red sun 'punctured' by the circular disk of Venus."

Astronomers will be looking to catch a glimpse of the elusive “arc of Venus.” The planet’s atmosphere refracts sunlight passing through the upper atmosphere during the transit, creating the impression that Venus is engulfed by a ring of fire.

"I was flabbergasted when I first saw it during the 2004 transit," astronomy professor Jay Pasachoff of Williams College told NASA Science. "A bright, glowing rim appeared around the edge of Venus soon after it began to move into the sun."

Amateur sky gazers will be able to record Venus’ path using an Android app called VenusTransit.

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Not just a pretty face

As well as providing a feast for the eyes, the rare transit of Venus across our Sun holds significant scientific value.

During Venus’ move, scientists will be able to conduct tests into the density of the planet’s atmosphere, collecting data to refine techniques to measure the atmospheres of other planets.

It could also help scientists to understand changes in the climate of our own planet. Venus and Earth are of similar size and orbit at roughly the same distance from the Sun, but their atmospheres are radically different.

Venus has a highly hostile climate, its atmosphere 100 times thicker than that of Earth and is largely made up of carbon dioxide.

The cocktail of gases in the planet’s atmosphere creates the strongest greenhouse effect in the solar system, producing surface temperatures of over 460 degrees Celsius.

"A human being transported to this hellish environment would be crushed, suffocate, desiccate, and possibly ignite," wrote Tony Phillips, with Science@NASA.

Observation of Venus’ previous transits has allowed scientists to calculate the size of our solar system and the distance between the Sun and the other planets orbiting it.

This time around it will provide scientists with pointers as to how to recognize a planet with an atmosphere that could potentially support life.