There won't be another until the 22nd century, when most of us won't be here. And remember the role of Salford and the wider north of England in the great astronomical event's history.

Next Wednesday, 6 June, isn't just the annual anniversary of D-Day. It's the last chance this century to see the Transit of Venus, one of the rarest and most important of astronomy's major - and generally understandable - events.

The planet Venus will be visible as a tiny black dot crossing the face of the sun, a process which allows the experts to fix the place of the planet Earth amongst the galaxies and within our solar system. This happens twice within approximately eight years every 120 years or so, and this is the second of a pair. The first of the two was on June 8 2004.

And it also shines glory on Salford. Look what playwright Eric Northey came across when he was walking through Lower Broughton in Salford. This plaque.

It commemorates a 17th century haberdasher from the area, William Crabtree, who was also an amateur astronomy. He and a friend, Jeremiah Horrocks, were the first two people to see the Transit of Venus, in 1639, after they had calculated when it would occur. As Northey says:
William Crabtree watching the transit of Venus in 1639 - one of the glorious murals by Ford Madox Brown in theGreat Hall of Manchester town hall.
 Photograph: Mike Pilkington/Manchester City Council
It was a colossal achievement for Salford over 400 years ago, in what was a hamlet in an obscure part of north-west Lancashire. It got me wondering: how did Crabtree get hold of Kepplers' Tables, which were published in 1632, so he could do the mathematics to observe the transit?

And, incidentally, correct Kepler, who also predicted the phenomenon but got the year wrong.

Northey was so intrigued by the plaque that he decided to research Crabtree's life and that of his collaborator, Jeremiah Horrocks, both of them ranked among the 'giants' on whose shoulders Sir Isaac Newton modestly said that he stood to make his own world-changing discoveries. From that research, he has written a play called The Transit of Venus which will be premiered in the 24/7 fringe theatre festival in July in Manchester.

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