The Reason for the Seasons

Here are the astronomical reasons for the seasons from The Old Farmer's Almanac. (Remember, astronomy is at the core of any almanac which is a "calendar of the heavens."

First, seasons are determined by the direction of Earth's tilt in relation to the Sun and the angle of the Sun's light as it strikes Earth.

• At one end of the axis is the North Pole; at the other, the South Pole.
• The axis is tilted at a 23.5° angle away from the Sun during winter in the Northern Hemisphere; it's the opposite in the summer.

In one year, Earth revolves completely around the Sun while rotating on an invisible axis, like a tilted, spinning top.

The Equator's Position

The equator is an imaginary line dividing Earth into the Northern and Southern Hemispheres. On 2 days each year, on or around March 21 and September 23, the Sun is directly above the equator. Here is how the equator relates to the seasons:

• In the Northern Hemisphere, spring starts on the March date, which is called the vernal equinox.
• Fall begins on the September date, which is called the autumnal equinox.
• Summer in the Northern Hemisphere begins on or around June 21, the summer solstice, when the Sun is directly above an imaginary line 23.5° north of the equator called the Tropic of Cancer.
• Winter begins on or around December 21, the winter solstice, when the Sun is above the Tropic of Capricorn, 23.5° south of the equator.
• The seasons are the opposite in the Southern Hemisphere.

Seasonal Facts

Here are some seasonal facts—the long and the short of it, as it were.

• The summer solstice is one of the longest days of the year in the Northern Hemisphere—and the day when there is no sunlight at the South Pole.
• The winter solstice is one of the shortest days of the year in the Northern Hemisphere—and the day when there is no sunlight at the North Pole.
• Daytime and nighttime on the equinoxes are not equal; this is a myth. However, within a few days of each equinox, there is a day with nearly equal daytime and nighttime. (This depends on the latitude.)

Find the dates for the solstices and equinoxes!