The library of Eratosthenes

Arras (FRANCE)

2007 by astro.perbosc

school : Ecole Lafontaine
city : Arras
country : France
address : rue Lafontaine
postal code : 62000
latitude : 50°17’ N = 50.283°
longitude : 02°44 ’ E = 2.733°
year : 2007


Really, we have been fortunate when we took these measurements! The weather was rather unfavourable, gray and cloudy, but the wind blew out gradually the clouds and let appear the sun intermittently. So, we seized these rare opportunities to take measurements of the shadow of the gnomon around solar midday, between 13:30 and 14:00. We set horizontally a wooden plan, and then perpendicularly, our gnomon. In that way, it was vertical. Then we noted precisely, the end of the shadow of the gnomon. Every 5 minutes, we measured the size of the shadow . When the weather was more favorable, the frequency of our measurements was shorter, in order to find the exact solar noon. That is simple: it occurs when the shadow ceases to decrease and when it starts to increase. The sun then reaches its highest point in the sky (zenith) and it is solar noon. Rémy - Mathilde - Antoine - Gaëlle.



Distance Arras - tropic of Cancer : 2981km
Angle : 26°33’= 26+33/60 = 26,55°

Circumference of the Earth = 2981 x 360 / 26,55 =40 420 km



The day of the videoconference with the Alexandria Library

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