20 March Equinox


    Activities for spring equinox:

    1. Measurements at schools from 17/3 to 23/3.

    2. Home measurement by students (if possible) on Sunday 20/3.

    3. Collaborative presentation on google slides about solstice and equinox.

    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 3 days before this date until 3 days after.
    The measurement procedure is thus adapted, limiting the problems of bad weather conditions as well as the fact that the day of the equinox falls on a Sunday.

    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 March 20 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.

    Argentina : | Chivilcoy |
    Colombia : | Guarne | Medellín |
    Puerto Rico : | Bayamón |
    USA : | Sault Sainte Marie |
    France : | Montcuq |
    Greece : | Aigio | Athens | Ilion | Stavraki |
    Poland : | Siedlce |
    Romania : | Bârlad | Busteni | Malovăț | Pogana | Slatina |
    Spain: | Benidorm |
    Morocco : | Tanger |
    Vietnam : | Hô Chi Minh City NT | Hoằng Giang |

    20 schools realized 46 measures of the angle of the sun from 17 to 23 March at solar noon.
    This angle decreases by 0.4° per day and is equal to the latitude on the day of the equinox (taking into account the measurement errors

    Download pdf

    Work process

    Work process

    Work process


  • March equinox

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    The importance of the shadow length- Iuliana Ciubuc-Busteni

    Application: Spring equinox march 2021 and march 2022