(Sen) - Astronomers all over the world are gearing up for that rarest of spectacles the Transit of Venus, which is now just four days away.
They will all be at the mercy of the weather. But there will be one man watching who can be absolutely certain of seeing it - because he is in space where there are no clouds.
NASA astronaut Don Pettit plans to take photos of the event on June 5th-6th, which will not be seen again for more than 100 years, from orbit aboard the International Space Station.
Sun-watching satellites are also being readied to monitor the Sun as the planet Venus passes in silhouette in front of it. But Don and his five colleagues on the space station will have a special ringside seat.
Veteran shuttle astronaut Mario Runco, of NASA's Johnson Space Center, said: "The Expedition 31 crew will be the first people in history to see a Venus transit from space, and Pettit will be the first to photograph one."
Astronauts were aboard the ISS for the last Transit in 2004 - they come in pairs eight years apart - but were unable to look at the event because they had no filters with them.
Today's missions by brave astronauts are being compared to the voyages into the unknown by sailing ships in the 18th century. English and French ships were sent on journeys lasting many months to remote islands in the South Pacific for the transits of 1761 an 1769, but had mixed fortunes with the weather.
NASA video describes Don Pettit's plans to record the Transit
The writer was present when the then NASA Administrator Michael Griffin made the comparison between manned spaceflight and those early sea voyages of exploration at the Royal Society in London in 2006.
Recognising that the journeys of 17th and 18th century European explorers often came at a high cost, including loss of life, Griffin said: "We are building on the heroic exploits of our forbears in their own missions of human exploration and scientific discovery."
He added: "We must be resolute in our convictions, and despite setbacks, we must recognize that progress through human exploration and scientific discovery is a goal worthy of the costs and risks of the enterprise."
Pettit, who is Flight Engineer on his mission, was aware the transit was coming up when he prepared to fly to the space station in December, so he packed a solar filter in his baggage.
He told NASA: "I've been planning this for a while. I knew the Transit of Venus would occur during my rotation, so I brought a solar filter with me when my expedition left for the ISS in December 2011."
Pettit will base himself in the ISS's Cupola, the European-built, seven-windowed observing room that allows the astronauts to look out at the Earth and stars, and take photos with a Nikon D2Xs camera fitted with an 800mm lens.