The organization of Eratosthenes in the International Year of Light has released the results of the measurements that were made by schools between the 14th and 25th of September 2015.

The data was collected by 174 schools from different countries, mostly from Europe and South America:  18 from Uruguay, 2 from Romania, 1 from Portugal, 5 from Peru, 1 from Morocco, 2 from Mexico, 1 from Italy, 1 from Honduras, 1 from France,  42 from Spain, 5 from Colombia, 45 from Brazil and 50 from Argentina.

Approximately 8000 students were involved in the activity and presented results about the size of the gnomon and the size of the shadow measured at solar noon.

With the results reported by schools the analysis were performed:

  1. Optimization of the NS component of distance and measurement day.
  2. Schools were paired maximizing the NS component of distance and considering that their measurements were made on the same day. Thus 200 pairs of schools were selected. 
  3. Radius obtained are calculated from the measurements reported by schools. 28 results were discarded because they were clearly out of range of possible measurements and therefore must be bad measurements or bad registration of the measurements.
  4. A histogram was compiled with the remaining 172 values that ranged between 5,500km and 7,000km.
  5. The average value of the data is R = 6.363km and standard deviation S = 316km. The standard error of mean Sp, S obtained by dividing by the square root of the number of measurements, it turns Sp = 22km.


Only statistical errors were considered, as  schools were not asked to report on the estimates of the errors of their measurements.  According tabulated values the Earth's radius is R = 6371 km, very close to the calculated value obtained from the data of the school measurements.

Eratosthenes project has been performed by the EAAE in association with other organizations since 1997.