Longitude

I realized: I have actually completed my second round of circling the globe.  Even though I am not back in Europe, I am more or less on the same longitude.

Here are the coordinates:

  • Cape Town, South Africa:
    33°55′ S, 18°22′ E
  • Tel Aviv, Israel:
    32°5′ N, 34°48′ E

I am some 16° west of Tel Aviv (my furthest point east on this trip), so I completed a full round.

I am fascinated by geography, and coordinates. The fact that my little phone can extrapolate, with the help of three satellites up in the sky, my exact location up to a few meters, is mind-boggling.

Notably considering that finding your exact coordinates was a vital, life-saving skill for centuries, for everyone who sailed the globe on a ship.

Seafarers could measure the latitude their were on pretty precisely by determining the degree the sun rose over the horizon every day. Knowing, however, where exactly they were as far as longitude is concerned (or: how far East or West) was an educated guess, for most of the time.

Ships disappeared, sank as they ran into riffs, veered off course for hundred of miles because they were not where they thought they were.

The problem was to determine when exactly the sun was in its zenith, and basically: when exactly was midday, at their current location.

They needed a precise clock that could show the time for example in London, and then extrapolate their position by using the difference when the sun hit its highest point in comparison to London time.

So three hundred years ago, the British Parliament passed the famous Longitude act in July 1714, which offered life-changing rewards to whoever could solve the ‘unsolvable’ problem of navigation at sea.

Eventually, the watchmaker John Harrison constructed a watch precise enough, and uninfluenced by the rolling movements of the ship, to determine location.

There’s a fascinating book (Longitude, by Dava Sobel) about this hero, who helped navigating the globe.

The Royal Observatory in Greenwich has an exhibition running till 4 January 2015 which I’ll miss unfortunately.

And just as I write this, I hear the daily cannon shoot, coming from Cape Town’s signal hill.

Every day at noon, a cannon is fired, since 1806, precisely to allow ships in the vicinity to re-set their chronometers to local time.

The ritual is one of Cape Town’s oldest traditions. The cannons used are the oldest guns in daily use in the world.