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The Reason for the Seasons

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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!

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By jose puca

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I love this site! I was

By charlottesmith

I love this site! I was brought up in Georgia, I lived in Victoria, Canada for 10 years, and now I am living in Bellingham WA. Welcome to the WET coast. I spent many summer trips to my Grand-parents home in South Ga., and my grandmother swore by that almanac, it was their planting bible. This brings back many great memories of life on their farm...picking blackberries, helping grandfather pick vegs. out of the massive garden, smelling the aromas from my grandmothers' kitchen, learning how to prepare, and can vegs. The giant storage closet where all the vegs. were store on shelves. All the beautiful colors in the jars. Looked like a garden rainbow! I am going back to that type of living of the land soon. Can't take the country out of me!

Today (9/23/12) I stumbled

By katestarr

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Kate Starr
Rockport, MA

So nice to read of 'normal'

By M John Burton on March 21

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