In 1760, a French astronomer named Guillaume le Gentil set out to India with the intention of observing the 1761 transit of Venus – that is, Venus moving over the Sun from Earth’s perspective. A great number of astronomers at the time were watching this from various places, as through triangulation, the combined observations would allow an exact calculation of the distance between the Earth and the Sun.
Unfortunately, a combination of bad weather and inconvenient military conflict in India meant that le Gentil failed to reach dry land in time for the transit. He knew, however, that there would be another such transit in 1769 (they occur in eight-year pairs which are then separated by more than a century – there were recent transits in 2004 and 2012). Rather than go home, he decided to hang around the Indian Ocean, and make sure he was good and ready for the next transit.
1769 eventually came round, and le Gentil was as ready as he could be. His instruments were all tested. The weather in the preceding days was perfectly fine. And on the day of the transit itself…it was too cloudy to see anything.
It’s a sad fact that if you’re interested in astronomy, unless you have a telescope on a high mountain or in Earth orbit, you are at the mercy of the weather – and sometimes, it deliberately seems to taunt you.
The last solar eclipse to be seen from Britain was on 11 August 1999; I was on holiday in France at the time and we set up a pinhole camera to try and observe it safely, but thanks to cloud cover, we only got the very briefest glimpse right at the beginning of the eclipse. Not very satisfying.
I was hoping for better with today’s eclipse, even though it wouldn’t actually be total anywhere in Britain; where I was, however, 90-95% of the Sun should be covered. Unfortunately, the weather was being badly behaved again. On Wednesday and Thursday, there was lovely sunshine – but the forecasters had already said that cloud cover was expected over much of England on Friday. And sure enough, on Friday morning, there it was.
According to the news, a lot of people in Britain didn’t manage to see anything at all; but in Preston, we did actually have some luck. Every now and then, we would see a slight break in the cloud, and the Sun would be shining through! My attempted pinhole camera proved a failure, but a combination of someone else having suitable glasses and the clouds just letting a little sunlight through meant that we got some good views right up until the peak around 9:35am.
At that point, it wasn’t exactly dark, but it did become very dusky, almost murky. Outside, all was quiet aside from a few bird calls, and it got pretty cold too. And then the clouds moved in again, completely covering the Sun for the duration of the Moon’s departure.
It may not have been a perfect view, but it was certainly something, and I’m very glad I was able to see it.