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What is the indian circle method?

I have been interested in shadows and the light of the sun, it can also be used for a perfect east west direction and thus navigation instead of a compass.

 

The Indian circle method allows you to accurately draw a line (red) running east-west with a simple set of equipment  with just a pole and the sun’s shadow (top image)

It involves plotting the path of the sun throughout the day using the shadow it casts from a rod or pole stuck vertically into the ground. As the sun moves through the sky, the shadow shifts across the floor like the point on a sundial.

If you plot the shadow’s position on the ground every half an hour, you are left with a curved ‘shadow line’.

The curvature of this line changes depending on the time of year because the sun sits at different points in the sky.

At the end of the day, with a curved shadow line drawn, you must wrap a short, taut piece of string around the vertical pole.

When moved around the rod in a circle, the end of the string should intercept two points on the shadow line. Drawing a new line through these two points creates a line running precisely east-west.

On the day of the autumn equinox it is possible to create a perfectly straight shadow line that runs east-west, with no need for the second, string line.The day is halfway between the summer and winter solstices, so day and night are of equal length, meaning the sun is perfectly centred in the sky.

Solar path:
We see in the above pictures that north gets casted a shadow (depending ofcourse wich hemisphere). However, if the pantheon design is used with an Oculus in the roof, the north (and east on setting sun) will get a sun spot,

 

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