Tuesday, 26 August 2008

Greenwich Means Time

I had a great day yesterday. We went to Greenwich Park to visit my Aunt Megan who lives conveniently close by. We met up in the park because she lives in an upstairs flat with access only via a steep flight of concrete steps which I have been unable to climb for the last 25 years. This August's frightful weather had a brief respite and provided us with an overcast but warm afternoon, even deigning to offer the occasional glimpse of sunshine. We even risked taking a picnic.

Greenwich Park is a World Heritage Site, and justifiably so. Situated on a steep hill over looking the Thames river and providing panoramic views of east London it has in it's grounds the National Maritime Museum and the world famous Greenwich Observatory, which gives the world the meridian – the hypothetical line marking Greenwich Mean Time. In the last year or so the observatory has been renovated and developed in to an outstanding visitor attraction and planetarium.


The observatory and visitor centre are free to enter and are packed with state of the art interactive displays and astronomical bits and pieces. While Polly and the boys wandered around touching hands-on virtual space age gizmos Megan and I snuck off to the Time Galleries to gaze at one of the most beautiful and important objects ever made – John Harrison's H4. The H4 is clockmaker Harrison's elegant solution to the Longitude problem, a problem that caused countless deaths at sea and had come to a head in 1705 when the brilliantly named but rather inept Sir Cloudesley Shovell ran a large proportion of the English navel fleet into the rocks off the Isles of Scilly costing 1,400 sailors their lives, because he didn't know exactly where he was.

To know precisely where you were in the days before satellites and GPS you had to know both your Latitude and your Longitude when out of sight of land. Latitude is relatively easy to determine using the sun and stars (1 say relatively as if I could calculate it myself if I chose too – I could, but not with out a copy of Google Earth) but Longitude was a whole different game of pin the tail on the watery donkey. To know your Longitude you need an accurate clock. Since clocks in the early 18th century relied on pendulums they weren't any good unless the sea remained absolutely flat. Since the sea is rarely absolutely flat you need a clock that isn't affected by motion or (equally importantly) changes in temperature. It is difficult to appreciate today how difficult it was to solve this fundamental problem. We take accurate time keeping for granted with our digital watches and atomic radio clocks but in Harrison's day it was considered an almost impossible problem to solve. Indeed, even trying to solve the problem was regarded as akin to inventing a perpetual motion machine might be today, the province of eccentrics and weirdos.


To encourage serious efforts the government offered in 1714 a massive prize of £20,000 (roughly £6 million or $12 million in today money.) Harrison eventually claimed the prize in 1773 after a life time of work and a series of upsets, petty officialdom and most significantly ever increasingly accurate clocks named imaginatively H1, H2, H3 and, of course H4. All four clocks are on display and they are truly beautiful.


After enjoying the wonders of the observatory we went to see a presentation in the planetarium about the life cycle of stars. With me being in a wheelchair we were swept in to the planetarium via a side door and given the best seats in the house. The show was quite awe inspiring as we journeyed through the galaxy visiting nebulae, pulsars and black holes, witnessing a supernova and the death our own Sun many billions of years hence. Fantastic.


It was the first day in a while I've felt up to doing anything so I'm glad it was such a good one.