Equinox and Solstice

During the summer the days are long and the Sun is high in the sky. The longest day is called the summer solstice.

During the winter the days are short and the Sun is low in the sky. The shortest day is called the winter solstice.

There are 2 days in between, one near March 21st and the other near September 22nd, where day and night are of equal length. They are called the vernal and the autumnal equinoxes.

Find the UK on the globes above. Compare the length of time that it is in sunlight and and shadow in each case.

This diagram shows the position of the Sun relative to the Earth on its (imaginary) yearly path on the ecliptic. Notice the equinoxes occur when the ecliptic crosses the celestial equator.

SS = summer solstice,   WS = winter solstice,   VE = vernal equinox,   AE = autumnal equinox

pic  Ian Britton - Freefoto.com

Why was it was very important to ancient peoples to know when these 4 events occurred?

How could they predict when the longest day would occur?