St Andrews, in the footsteps of James Gregory September 21, 2008
Posted by astroed in Astronomy, Education.Tags: history, stargazer, telescopes
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On Saturday we travelled out from Edinburgh to the ancient kingdom of Fife, just north of the Firth of Forth. After a pleasant stop at Elcho Castle we arrived in the University city of St Andrews, otherwise famous of course for golf. Our goal was to visit some places in town associated with the Scottish astronomer and mathematician, James Gregory (1638 – 1675) who was Regius Professor of Mathematics at the University.
Gregory has often been compared with Isaac Newton but unfortunately died tragically young at 36 years old before his achievements were fully recognised.
Gregory is today commemorated by the type of reflecting telescope that bears his name, the Gregorian. In Gregory’s time telescope makers were still making telescopes from lenses – refracting telescopes. These suffered from problems with chromatic aberration that split the light into component colours when looking at brighter stars and planets. The other issue was that in order to get higher magnifications the refracting telescopes used longer and longer focal length. This resulted in ridiculously long telescopes that were increasingly hard to handle and point successfully at stars.
Whilst Newton is credited with building the first successful reflecting telescope, that is one that uses a primary mirror instead of an objective lens, there is strong evidence to support the case that Gregory had built an earlier one in early 1663 using a concave primary and a concave secondary. A year earlier he had published his work Optica promota that was well received. Gregory also developed an early form of what we now call calculus, another discovery normally attributed to Newton and Leibniz.
Joseph Knibb’s split-second clock, used by James Gregory.
In St Andrews we were fortunate to visit the Senate House that houses the clocks built by the clockmaker Joseph Knibb and purchased by Gregory in 1673 for timing his observations. One of these early pendulum clocks was the first to record split-seconds. It had a mechanism that used 1/3 second motions. Gregory conducted his observations from the room next door, now the St James Library. He used a transit telescope pointing south out of one o the windows. The transit line is now hidden beneath the carpet but the bracket on which his transit telescope was mounted is still visible through the window. Unfortunately a building has now been built adjacent to it, blocking the view that Gregory would have once had.
Bracket (at left) that Gregory used for his transit telescope.
In the ruins of St Andrews Cathedral, once one of the largest in the British Isles is the imposing Rules Tower. The university had suggested to Gregory that he could build his observatory on the top of the tower but declined, probably wisely given the task he would have faced lugging his equipment to the top!
Earlier in the week I had come across one of the first successful gregorian telescopes built many years later and now housed in the National Museum of Scotland.
Gregorian telescope from National Museum of Scotland.
Before we departed St Andrews we were also fortunate to visit the modern observatory of the university led by Professor Andrew Collier Cameron, Professor of Astronomy at the university. Here we inspected the 40” Schmidt-Cassegrain telescope now called the Gregory Telescope. This is still in use for exo-planet transit studies. It was actually only the second telescope of this design ever built. The first, a half-size prototype was also built for the observatory and housed in a nearby dome but has since been dismantled.
Dinner was an extremely enjoyable meal at The Hideaway in Dunfermline, run by Fred’s son-in-law. Our dinner guest was none other than the Astronomer Royal for Scotland, Professor John Brown from the University of Glasgow. He entertained us with some magic tricks for black holes, interstellar dust and cosmic strings. A fine way to end such a wonderful day.
Professor John Brown, Astronomer Royal for Scotland having fun with cosmic strings!
Questions:
- Why was the invention of the pendulum clock important for astronomers in the second half of the 1600?
- What are some advantages of a reflecting telescope over a refracting (lens) telescope?
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