Venus made a rare transit across the face of the Sun on Tuesday, giving stargazers from Australia to the Middle East and Africa a celestial view that no living person had seen before.
To the fascination of people around the globe armed for the occasion with telescopes, pinhole cameras and special dark glasses, Venus appeared at 0520 GMT: a small black dot on the lower edge of the Sun starting its six-hour transit.
"We are watching the first transit of Venus since 1882 - until this morning no one alive has ever seen this event," said Dr Robert Massey of Britain's Royal Observatory in Greenwich as more than 100 people gathered in the courtyard of the London landmark to witness the phenomenon.
Banks of photographers with telephoto lenses and television crews captured the event. People queued patiently as parents lifted small children to gaze into telescopes set up in the courtyard of the observatory on a clear, warm morning.
Others used special glasses handed out by staff to see the event.
"It is very mysterious," said Japanese tourist Hiroyuki Narasawa, after peering up at the sky through a cardboard tube and camera.
Scandinavian airline SAS offered dark glasses to about 3,500 travellers on Nordic flights to watch Venus from above the clouds. It was partly cloudy over sections of northern Europe.
RIGHT TIME, RIGHT PLACE: On the other side of the globe in Australia it was already afternoon when 40 amateur astronomers gathered at the home of Jos Roberts north of Sydney.
"I feel very privileged to be alive at the right time, to be in the right place, to have no clouds or monsoons," said Roberts who toasted the event with champagne with his colleagues.
In the Middle East, schoolchildren gathered on the hills outside Beirut to watch the passage through dark glasses.
For the Americas, however, the complete transit was only partially visible.
The Venusian transit only occurs four times every 243 years. Two are in December, eight years apart, and then 121.5 years later there are two June transits, also eight years apart. After another 105.5 years the cycle begins again.
The next passage will occur in 2012 but will not be visible in many parts of the world.
In the past, scientists calculated the distance of the Earth from the Sun, the astronomical unit (AU), from measurements of the duration of the transit of Venus made from widely separated latitudes.
England's Captain James Cook travelled to Tahiti on a special expedition to make observations during the 1769 transit.
This time, too, observers around the world will be timing the transit and repeating the historic calculations.
"It's the different timings (from different locations) which allow you to measure the distance (to Venus)," said John Mucklow of the Astronomical Society of Southern Africa who used an old telescope mounted on a wooden tripod to watch the spectacle from the roof of a hotel near Johannesburg.
But Dr Robert Walsh, of the University of Central Lancashire in northern England, had arguably the best viewing position - the bedroom of British astronomer Jeremiah Horrocks who was the first person to observe a transit in 1639.
"To see what he saw from a specific point is very exciting indeed," he said.