Due to the Earth´s tilted axis, the angle of the Sun's rays at given latitudes continuously changes during the year.
The first calendars and time-measuring instruments were already used by ancient Eastern civilisations.
The rise and drop of sea levels caused by the gravitational force of the Moon.
The Earth is divided into 24 time zones. Standard time is the time used within time zones.
Place historical events on the time spiral.
During its orbit around the Earth, the visibility of the Moon's illuminated part constantly changes.