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Days and nights over the year HTML5


The length of a day by comparison with that of a night depends on the date and the place. This is the result of the sphericity of the Earth and its inclination in relation to the Sun.

The part of the Earth which lies in the shadow of the Sun corresponds to the night zone. This zone is a half sphere but, when transferred to the plane projection of a flat world map, this shadowed zone takes on a complex shape that changes in the course of a year.

This animation enables us to simulate these changes and to illustrate the following phenomena:

  • The daylight period is longer in the northern hemisphere in the summer.
  • Summer in the northern hemisphere corresponds to winter in the southern hemisphere and vice versa.
  • The summer and winter solstices are the points in the year where there is the greatest difference in the durations of day and night.
  • The equinoxes at the end of March and the end of September are the points in a year where the length of the day equals the length of the night (12 h) everywhere on Earth.
  • The lengths of day and night are equal for all points lying on the Equator.
  • The polar regions are subjected to a polar day (summer) or a polar night (winter); these can last up to 6 months.

Click on the  button to speed up the passage of time.

Click and drag the cursor to change the date.

Click and then pivot the terrestrial globe to change the viewing angle.

Learning goals

  • To understand why the length of daytime varies in the course of a year.
  • To show the relationship between the terrestrial globe (spherical) and its projection onto a map (planar).
  • To define equinoxes and solstices.
  • To justify the use of time zones to define a local time at any place on Earth.

Learn more

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