Activities for automn equinox:

1. Measurements at school from 18/9 to 24/9.

2. Experimental activities > Solar noon: Locate the positions of the extremity of the shadow during the day, to draw the equinox line

Work process

To allow the participation of the largest number of schools, measurements are not only carried out on the day of the equinox, but also from 4 days before this date until 2 days after.
The measurement procedure is thus adapted, limiting the problems of bad weather conditions.

The collaborative measure
During these 7 days, the partner schools exchange the results of their measurements of the height of their gnomon and the length of its shadow at solar noon, which define the angle of the sun at that moment.
It is not necessary for these schools to be located on the same meridian: These measurements being synchronized at solar noon, it is indeed the distance between the parallels passing through these 2 schools which is used to calculate the circumference of the Earth.

The Eratosthenes historical method
The historical measurement of Eratosthenes took place during the summer solstice, with Syene (Tropic of Cancer) as a reference, ie the place where the Sun is at its zenith on this date. These conditions are also fulfilled on the day of the equinox for all places located on the equator.

Latitude and angle of the Sun
The measurements of September 22 but also those carried out during the week, thanks to a regression calculation, make it possible to verify that latitude and angle of the Sun are equal on the day of the equinox.

AMERICA (7)
Argentina : | Chivilcoy |
Brazil : | Méier | Del Castilho | Pelotas |
Colombia : | Guarne |
Puerto Rico : | Bayamón | San Juan |
EUROPE (7)
Greece : | Larissa |

Moldova : | Salcuta |
Romania : | Baia Mare | Busteni | Galati | Malovat |
Spain : | Ubeda |
 

14 schools realized 25 measures of the angle of the sun from 18 to 24 September at solar noon.  This angle increases by 0.4° per day and is equal to the latitude on the day of the equinox (taking into account the measurement errors)

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