It doesn’t look like much, but this piece of paper took centre stage in our experiment yesterday to measure the School’s longitude.

The paper was left in the garden on the hill with a stick pointing directly upwards where you can see the circle to the left of the page (click image below to enlarge). That stick cast a shadow, and at various times of the day the class and I marked the length of the shadow.

Drawing a curve through the points, we then measured where the curve was the shortest distance from the stick. This then told us the time where the sun was at its highest: solar noon.

Solar noon in Llanycefn yesterday was 1:15:45. We made it 1:17. This is a difference of 75 seconds! Not bad.

Solar noon in Greenwich yesterday (where the Prime Meridian (0 degrees) is) was 12:56:43.

The difference between solar noon in Greenwich and in Llanycefn (by our measurements) yesterday was 20.25 minutes. As the earth rotates 15 degrees every hour, 20.25 minutes means that from the time the sun was highest in Greenwich to solar noon in Llanycefn, the Earth turned 5.0625 degrees, giving Llanycefn a longitude of 5.0625 degrees west. Llanycefn’s actual longitude is 4.7890 degrees west, meaning our measurements were out by approximately one third of a degree. Pretty accurate really for a scruffy bit of paper!

All of this helped me to explain how HMS Beagle was surveying the South American continent in 1831, collecting longitude measurements using 22 chronometers onboard. It supported map-making, and has given some context as to why Charles Darwin was collecting flora and fauna in the southern hemisphere prior to writing The Origin of Species.