An early and spectacular attempt to measure parallax

Then came the Monument. It was supposed to be a grand acknowledgement of the fire, but at the time, “what Hooke really wanted was to build a very long telescope” says Maria Zack, a mathematician at Nazarene University, California. In the end, he decided to combine both.

The Monument to the Great Fire of London consists of a towering, 202-foot (61-metre) stone column, decorated with dragons and topped with a flaming golden orb. On the inside, a striking spiral staircase stretches all the way to the top, twisting up like the peel of an apple carved in a single, continuous ribbon.

Back in the 17th Century, scientists were still arguing about whether the Sun revolved around the Earth or the other way around. Like all rational people today, Hooke was thoroughly convinced by the latter. But no one could prove it. In theory, it should have been easy, thanks to “astronomical parallax”, an apparent shift in the position of one object, against a backdrop of another.

If the Earth changes its position relative to the stars, while circling the Sun – then they should appear to jump from one place to another over the course of a year.

The catch is just how tiny these movements are. Take Gamma Draconis, a giant orange-coloured star around 900 trillion miles (1.4 quadrillion km) away. Instead of measuring the movement of objects in the sky, from planets to satellites, in metres or inches, astronomers divide up the heavens like the face of an imaginary clock. Every six months, the star moves north or south in the sky at a scale equivalent to the hands moving 22 ten-thousandths of a second. To magnify parallax enough to see it, you need a very large telescope indeed.

“He was trying to keep the two lenses aligned, 200ft apart, with only limited ways to anchor them to the telescope,” says Zack. Worse still, the Monument is next to Fish Street Hill, which was the main route to London Bridge at the time. This was one of the busiest roads in London, mere metres from his highly sensitive scientific experiment. In the end, vibrations from the traffic ruined everything.


http://www.bbc.com/future/story/20170810-the-medieval-lab-hidden-inside-a-famous-monument