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Star Gazing

I was reading an article recently about the Gran Telescopio Canarias, and it’s observatory based in the Canary Islands, which is currently the world’s largest single-aperture optical telescope. I must admit to knowing very little about telescopes and their workings, but I do know that this one is a light refracting telescope. I also know that the length of this Gran Telescopio is just under 24 meters (nearly 79 feet). It was developed by the Spanish and Mexicans and I’m sure they are rightly proud of it.

But I know of a telescope who’s size would have made todays record holder look like a child’s toy, and one that was in operation 360 years before this record holder was built. It’s in the City of London and parts of it can be seen today. Take a look at the photograph below and see if you can spot it,

Do you see the building on the right just by the delivery van? No I’m joking, it’s actually the tower right in the centre of the picture. Dear reader, I can hear you saying “but surely that’s the Monument, built as a memorial to the Great Fire of London in 1666“, and you would be right, it is.

Robert Hooke

Sir Christopher Wren

Designed by Sir Christopher Wren and Robert Hooke the monument was erected between 1671 and 1677, but what is not widely known is that Wren and Hooke built the monument to double-up as a scientific instrument. It had a central shaft meant for use as a zenith telescope, used to observe stars that pass directly overhead. A lens was placed at the top of the tower and the observer would sit in an underground laboratory which was accessible through a hatch in the floor, now in the present-day ticket booth. The total length from lens to the laboratory was in excess of 62 meters (203 feet). However the use of the telescope to obtain clear images was hampered by the vibrations from heavy carts on the surrounding cobblestones, and the movement of the tower from the wind which made the lens shake, rendering the experimental conditions unsuitable. However the pair had also designed the steps used to climb the tower to be exactly six inches in height, which allowed them to undertake experiments concerning barometric pressure.

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