When I returned to Cambridge University's Engineering Department from the USA in 1984, my wife and I bought a historic and wonderful house some ten miles south of Cambridge. It was built around 1520, a date that could be substantiated to within a decade by the form of the oak beams that comprised its floors and ceilings. These had been shaped by iron blades that only lasted about ten years. Being someone of the present rather than the past I had not previously been much preoccupied with history, but living in the splendid oak structure – like a fine sailing vessel that had gone aground – inspired me to wonder what had preoccupied the technologists and scientists of that age.

In my search I discovered that on 24 August 1563 a ‘conjunction’ took place of the planets Saturn and Jupiter. The two appeared so close together in the sky that they seemed to merge together. This rare occurrence was of great importance in an era when it was widely believed that exceptional astronomical events both influenced and predicted worldly happenings.

The problem was that the very best minds of the period, in Europe at least,were quite unable to calculate exactly when the conjunction was to take place. Some calculations were at least a month out. The best were inaccurate by days. Given the science and technology of the period, such inaccuracy is easy to understand. There were no reliable and accurate clocks.