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Astronomers prepare for rare Venus transit

By Alisha Lewis

Published: 5:54PM Friday March 16, 2012

  • Venus transit across the Sun (Source: ONE News)
    Venus transit across the Sun - Source: ONE News

New Zealand is in for an astronomical treat this June when the country will be perfectly positioned to see the planet Venus transit across the face of the Sun.

For six hours on Wednesday June 6, from 10.15am to 4.43pm, a significant black dot will be visible as Venus moves across the Sun's surface.

However the president of the Auckland Astronomical Society, Grant Christie, said that what people will be able to see on the day depends on the weather.

"That's the crucial thing - if the skies are clear, we'll get a nice view," Christie said.

Taking place only when Venus passes directly between the Sun and the Earth, the transit happens in pairs separated by eight years.

Each pair then occurs at alternating intervals of 105 and 121 years, making this an incredibly rare event.

When it last happened in 2004 New Zealand was not positioned to view it and Christie said this means the upcoming event is a "once in a lifetime opportunity for most people".

"We're really well placed this time," said Christie. "Last time, New Zealand just missed out, although it was visible just before sunset in Australia. But this time we get to see it in its entirety."

However Auckland's Stardome Observatory astronomy presenter Peter Felhofer said it's crucial that people take precautions before viewing the phenomenon.

"We need to stress that people do need to use solar telescopes or filters."

Felhofer said another option was to view the transit as a projection through a piece of board or card.

Stardome has already begun preparing for the event, stocking up on solar glasses which Felhofer said people should not confuse with regular sunglasses.

"These have a very, very high degree of filtering so that it is actually safe to look at the Sun. Do not use normal sunnies - you will still cause yourself damage."

Christie said that while the rarity of the event is bound to draw attention - the next one won't happen until 2117 - the transit's historical significance is what's really important.

"For years they were considered the only way to work out the distance from the Earth to the Sun, said Christie.

"Once you know the distance of the Earth to the Sun you can work out the distance from the Earth to stars, and then to other objects in the galaxy and then of course to other galaxies themselves."

In particular, the transit of Venus has special historical significance when it comes to New Zealand. Captain Cook was dispatched in 1768 with the primary mission of observing the transit of Venus from the Pacific.

The only other planet to make a similar transit is Mercury - the other 'inferior' planet, meaning it is closer to the Sun than Earth.

Felhofer says that Captain Cook was sent further south, to New Zealand, because it had been calculated that there would be a transit of Mercury visible there not long after the transit of Venus.

"So today if you go to the Coromandel, there's a place called Mercury Bay, that's where Captain Cook observed the transit of Mercury."

These days however there is not much more to be learned from transits.

"It's more a phenomenon," said Felhofer. "Today we understand all the science that is involved, we have a lot more information about a planet like Venus - what its atmosphere is made up of and all that."

However, Christie said scientists still remain interested.

"Scientists will still be observing and watching what happens - examining the sun's light shining through Venus' atmosphere. There are always still things that could be learned."