Talk - Lewes Astronomers

“I call my talk ‘how long is a piece of string’ because it’s all about man’s attempts throughout history to measure how far the earth is from the moon and the sun,” says John Stapleton. John, the Secretary of the Basingstoke Astronomical Society, will be addressing his talk, which is ‘historical rather than technical’ to the layman. “The Greeks worked out the relative proportions of distance between the planets, so they knew that if they worked out one figure, they could then work out all the others. The quest for this measurement became the most important theme of astronomical research for over a thousand years. My story is how they went about that.”

And how did they go about it? “In the Middle Ages they started using the Parallax method,” he says. “This is the idea that if you close one eye and cover the image of the edge of the door with your thumb, when you open your eye it appears to have moved,” he explains. “This is to do with angular distance. The theory was good, but it didn’t work because their instruments weren’t up to it. When Galileo discovered the moon of Jupiter they tried measuring the movement of the moons across the face of the planet. The only trouble is they had no idea how big Jupiter really was.” John takes us right up to today, when Nasa are bouncing lasers off the moon and, with the use of orbiting probes, we can measure the distance to the sun to the accuracy of a metre or so. And how far is that? “93 million miles, in round numbers,” he says. “On average, that is.” AG