Eratosthenes

Arras

March 2008

Flag City Country School Latitude (°) +N/-S Longitude (°) +E/-W
Arras France Ecole Lafontaine 50.283 2.733
Date Gnomon Shadow Angle
March 24 100 cm 120 cm 50°11’ = 50.194°


The weather was so bad , that we just realized measurements between 9:10 am to 11:20 am (Central European Time).
We marked with a paint spot the extremity of the shadow of the gnomon.
Those 14 points were drawing a line: It happens only twice during the year, on the equinox days.

So we could make an estimation of the shadow length at solar noon:
120cm for a 100cm high gnomon.
The angle of the sun is 50°11’ = 50,184°
This angle is close to the latitude of our city : Arras (50°17’N)

We started calulating the circumference of the Earth with Equator as virtual partner.

The latitude of Arras is 50°17’=50.283°

So the calculated distance to the Equator is 50.283 * 111.1 = 5,567 km

We found for the circumference: 5,587 * 360 / 50.184 = 40,079km


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