Wednesday, April 15, 2020
This is the sundial in the Great British Garden in the Olympic Park.
It's an example of an analemmatic sundial.
The first analemmatic sundial was laid out in the French town of Bourg-en-Bresse in 1513.
Around the edge are two rings of numbered discs, each in the shape of an ellipse.
The outer ring is for GMT and the inner ring for BST.
In the centre is a strip aligned north/south on which the months of the year are written.
Stand on the correct month and your shadow tells the time.
Different months need different positions to match the declination of the Sun.
This is the angle between the rays of the Sun and the plane of the Earth's equator.
At the equinoxes declination is zero, which is why March and September appear in the centre of the strip.
At the solstices declination is at its maximum, which is why June and December appear at opposite ends.
It works too. Here's my shadow at quarter to nine in the morning while standing on 'April'.
I should go out and test it again today.
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