About Earth's Seasons, Equinoxes and Solstices

The Earth revolves around the Sun once a year and rotates daily on its axis, which is inclined at 66½° to the orbital plane and always points into space in the same direction. At midsummer (N) the North Pole tilts towards the Sun, six months later it points away and half way between the axis is at right angles to the direction of the Sun (below).

The Seasons - Summer

The Sun's highest position in the sky is at the summer solstice. In the Northern Hemisphere this occurs about June 21-22. At this time the North Pole tilts directly towards the Sun. It is the longest day of the year and the start of a season marked by warmer temperatures, lush plant growth, and for humans - weekends at the beach.

The Seasons - Autumn

As the Earth moves away from the point in its orbit where summer solstice occurred, the days become shorter. At autumn equinox in the Northern Hemisphere, which comes about September 21-23, the nights are as long as the days. Deciduous trees begin to lose their leaves, birds migrate to warmer climes, and humans begin wearing sweaters.

The Seasons - Winter

Winter arrives with the winter solstice, when the Sun is at its lowest point in the sky. This is the shortest day of the year; in the Northern Hemisphere, the solstice occurs about December 21-22. Temperatures are at their coolest in this season, many living things hibernate and humans don skis and ice skates as well as very warm clothes.

The Seasons - Spring

Following winter solstice, the days gradually lengthen. On the spring equinox, which comes about March 21 in the Northern Hemisphere, the Sun is midway between its positions on the two solstices. The days are as long as the nights. It is the start of spring. Trees begin to bud, birds migrate to their nesting grounds, and humans plant crops and trees.

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