Venus makes rare trek across the Sun

Planet Venus has put on a show for skywatchers by moving across the face of the Sun as viewed from Earth.

The transit was a very rare astronomical event that would not be seen again for another 105 years.

Observers in north and central America, and the northern-most parts of South America saw the event start just before local sunset.

The far northwest of America, the Arctic, the western Pacific, and east Asia witnessed the entire passage.

While the UK and the rest of Europe, the Middle East, and eastern Africa waited for local sunrise to try to see the closing stages of the transit.

Venus appeared as a small black dot moving slowly but surely across the solar disc. The traverse lasted more than six and a half hours.
Projection method used in Canada Special events provided safe ways for the public to see the transit

Some of the best pictures of the event were provided by the US space agency's (Nasa) Solar Dynamics Observatory, which studies the Sun from a position 36,000km above the Earth.

"We get to see Venus in exquisite detail because of SDO's spatial resolution," said agency astrophysicist Dr Lika Guhathakurta.

"SDO is a very special observatory. It takes images that are about 10 times better than a high-definition TV and those images are acquired at a temporal cadence of one every 10 seconds. This is something we've never had before."

Many citizens keen to observe the transit first hand attended special events at universities and observatories where equipment for safe viewing had been set up.

In Hawaii, one of the best places to see the whole event, the university's Institute of Astronomy set up telescope stations on Waikiki beach.

"We've had 10 telescopes and the queues have been 10 deep to each telescope all day long," said the institute's Dr Roy Gal.
A man poses for a photograph as people queue up along the Hong Kong harbour waterfront to look through a telescope They queued to see the transit by the waterfront in Hong Kong harbour

"It's a great opportunity to get people excited and teach them stuff. I was hoping for a big turn-out, and it's been fantastic," he told BBC News.

Joe Cali viewed the transit on the edge of the Outback in New South Wales, Australia, another ideal vantage point.

"It is exciting. It may look like just a black dot on the Sun but if you think about it, it's one of the few times you get to see a planet in motion," he said.

UK skywatchers had to deal with quite extensive cloud conditions across the country.

"We've had total cloud and rain," said Brian Sheen from the Roseland Observatory in Cornwall.

"But we've been improving our chances by connecting with the Shetland Islands and the people up there have done rather better than we have. We've been seeing the transit through [a feed] of one of their telescopes," he explained.

Scientists observed the transit to test ideas that will help them probe Earth-like planets elsewhere in the galaxy, and to learn more about Venus itself and its complex atmosphere.

As part of Horizon's Transit of Venus programme, science presenter Liz Bonnin explains what the transit of Venus is and why it is such a rare event

Venus transits occur four times in approximately 243 years; more precisely, they appear in pairs of events separated by about eight years and these pairs are separated by about 105 or 121 years.

The reason for the long intervals lies in the fact that the orbits of Venus and Earth do not lie in the same plane and a transit can only occur if both planets and the Sun are situated exactly on one line.

This has happened only seven times previously in the telescopic age: in 1631, 1639, 1761, 1769, 1874, 1882 and 2004.

The next pair will not now occur until 2117 and 2125.