Astronomers and historians will open a window on a past triumph of science when they gather in a Lancashire manor house to witness the transit of Venus.
People around the world will try to catch a glimpse of the rare phenomenon, which no living person has witnessed, on June 8. In Britain, the transit is expected to begin in the early morning.
Scholars at a conference at the University of Central Lancashire, including TV astronomer Patrick Moore, plan to watch it from the room in Carr House from which it was supposedly first observed by Jeremiah Horrocks, a 20-year-old self-taught astronomer, in 1639.
A transit of Venus involves the planet's passing directly between the Earth and the Sun. The planet's tiny disk, equivalent in size to a pound coin at 85m distance, will take less than six hours to cross the Sun. It can be observed only indirectly, by projecting its image through a pinhole on to a screen.
Horrocks was the first to accurately calculate Venus' path and to work out when the next transit would occur. The event was ultimately used to help calculate the size of the solar system. The most recent transit occurred in 1882.
The International Astronomical Union-sponsored meeting will bring together 100 astronomers and historians to discuss past and present attempts to measure the solar system and the universe. The precise measurement of astronomical distances allows scientists to probe cosmic mysteries, ranging from the motion of the planets to the expansion of the universe.
Don Kurtz, co-chair of the conference's scientific organising committee, said the mix of historians and astronomers would provide unique insights.
"Too often, scientists get together without understanding the history behind their work, while historians get together without understanding the science," he said.
Allan Chapman, a historian of astronomy at Oxford University, noted:
"History runs into the very bone marrow of science in that you base your work on someone's previous findings. The modern approach to astronomy, at least in Britain, began that November afternoon in 1639 when Horrocks and his friend William Crabtree observed the transit of Venus."
Myles Standish, a principal member of the technical staff at Nasa's Jet Propulsion Laboratory in the US, said that modern techniques had enabled his team to measure distances within the solar system with great precision.
Venus will be 43 million km away on June 8, but its position is known to within a few hundred metres. Such accuracy is essential for interplanetary navigation.
Dr Standish, who will address the conference, said: "Things have moved on a lot since Horrocks observed the transit of Venus."
More than 300 people have pledged to record the exact times of the transit as part of a worldwide campaign organised by the European Southern Observatory.