On summer solstice eve I was able to photograph the alignment between the circle and the setting sun over Brown Willy and the setting sun lines up well with the prominent hill. Even taking into account that in prehistory the sun wouldn’t set in exactly the same position today (it would be 2 solar discs to the right in the photo above) there is a clear correlation between the two.
Craddock Moor circle isn’t the only prehistoric site where you can watch the summer solstice sunset over Brown Willy and there is an extended line of monuments across the moor where this can be seen. These include the standing stone above the Hurlers and at Goodaver circle.
Craddock Moor circle has another alignment this time with the rising summer solstice sun and Stowe’s Hill. The winter solstice sunrise and sunset have a loose arrangement with the barrows on Caradon Hill and a rolling sunset down Tregarrick Tor. This makes it a very remarkable solstice-aligned circle.
On solstice eve I was treated to sun dogs forming either side of the sun which was a magical sight which kept me watching the skies before the sunset.
How did we weigh the Earth (and why did this go beyond simple curiosity)? This may be a question people asked themselves during childhood, and have not considered since. Yet it is a question a small group of scientists, including myself, have returned to as we research experiments conducted in the 1820s in a Cornish mine to measure the acceleration due to gravity of the Earth.
In 2022 our intention to re-create the mine experiments by building a replica Kater invariable pendulum and taking it down a Victorian mine in west Cornwall to make measurements of gravity. We will set the pendulum in two locations, one overground and one underground, and time the swing of the pendulum in both locations. The difference in the rate allows us to calculate the amount of gravitational pull on the pendulum, as the underground pendulum will swing at a slower rate. The original experiment was conducted by George Biddell Airy and William Whewell in the deepest mine in England, Dolcoath. This has unfortunately closed and the lower recesses are flooded, so we are using a mine named Rosevale, which gives us a difference of 250 metres between the overground and underground stations. Although Rosevale is not as deep as Dolcoath (700 metres at the time of the original experiment), it gives the opportunity to explore how the experiment was conducted in what can only be described as less than ideal conditions. Mines are dirty places which can be excessively damp and hot. During the original experiment the scientists would have had to contend with vibrations and noise from the working environment, making their achievements all the more significant.
Why is this all important now you may ask? Yes, simple curiosity does play into this but we find ourselves in a time when the power of gravity is something we have learnt to manipulate and overcome. There are frequent launches into space and discussions of journeys to far-flung destinations such as Mars. Without the arduous and at times dangerous early experimentations into measuring the gravity of the Earth untaken by Airy, Whewell and others we could still be stuck without the knowledge to reach beyond our own planet. Therefore we think it is the perfect time to highlight the work they undertook and their achievements in what was an important building block for us to travel into space.
Blog post first appeared here –