MILLIONS of people took part in an international festival of celestial observation yesterday and witnessed what no living person has seen before: the passing of Venus across the Sun.

At 6.19am British Summer Time the Earth’s closest planetary neighbour edged on to the Sun’s bright disc and began to creep slowly over its face for the first time in 122 years.

Over the next six hours millions of observers across five continents, from Sydney to New York, witnessed something that passes entire generations by: the transit takes place four times in 243 years, in pairs of dates separated by around eight years or more than a century. The next will be in 2012, but after that it will not happen again until 2117.

In Britain the hottest day of the year so far provided near-perfect watching conditions for most. Only in parts of Scotland and Northern Ireland did blankets of cloud obscure the view.

Staff at the Royal Observatory in Greenwich said they were astonished at the numbers wanting to use its telescopes and solar viewers.

The observatory’s entire stock of 1,000 eclipse glasses had been handed out by 9am and more than 3,000 had seen the transit there by the time Venus completed its passage at 12.23pm.

Robert Massey, a senior Greenwich astronomer, said the numbers watching worldwide would outstrip even the total eclipse of 1999.

While millions of tourists travelled to the narrow band over Europe and Africa where that event was visible, the whole transit of Venus was seen from Europe, Asia, Africa and Australia, while eastern parts of North America caught its final moments.

“This is the largest mass astronomical event there has ever been,” Dr Massey said. “Total eclipses attract a lot of people but they are a lot more localised. Today, millions of people all over the world have all been seeing precisely the same thing. There is a global communal feeling about this event that is quite wonderful.

“The grandeur of a total eclipse is something unparalleled (because) it is the most magnificent astronomical phenomenon. But the transit of Venus is one of the very rarest. Until today there was nobody alive who had seen one.”

The transit of Venus takes place only when the planet’s orbit takes it directly between the Sun and the Earth, an event that occurs at intervals of 8, 121.5, 8 and 105.5 years. Another transit will happen in 2012 though it will not be visible from Britain.

The phenomenon has been observable and predictable only since the invention of the telescope in 1608. It was first seen on November 24, 1639 by Jeremiah Horrocks, a 20-year-old self-taught Englishman who calculated that one was due and watched it from Carr House in Much Hoole, near Preston, Lancashire.

Further transits took place in 1761, 1769, 1874 and 1882. The next one to be visible from Britain will be in 2247.

The hundreds of people who gathered at Carr House yesterday had fine conditions.

Professor Gordon Bromage, of the University of Central Lancashire, who organised the viewing, said: “They were elated, literally jumping with excitement . . . yelling ‘I’ve seen it, I’ve seen it!’

Venus was about 43 million miles away from Earth yesterday and appeared as a black disc about 30 times smaller than the Sun.

Previous transits of Venus have led to some landmark scientific discoveries. The distance between the Sun and the Earth — 93 million miles — was first calculated with approximate accuracy during an 18th-century transit. And Captain James Cook reached Australia and New Zealand when dispatched to the South Pacific to observe the transit of 1769.

HALLEY THEORY

IN 1716 Edmond Halley, the Astronomer Royal based at the Royal Observatory in Greenwich, first established that the transit of Venus could be used to measure the distance between the Earth and the Sun.

He never found out for certain that he was right: Halley, who is best known for the comet that bears his name, died in 1742 without witnessing a transit, and it was left to his successors to calculate that the distance — known as an astronomical unit — stands at 93 million miles.

Yesterday a group of amateur astronomers reconvened at Greenwich, just to check the maths. As Venus touched the edge of the Sun at 6.19am BST, observers from the Flamsteed Astronomical Society sought frantically to record the precise moment of “first contact”.

A few hours later, the calculations were complete. Fortunately, Halley and the astronomers who put his theory into practice were right: the astronomical unit will live to fight another day.

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