The Astronomical vs. Meteorological Seasons

If someone asked you when each of the seasons occurs, how would you respond? Your answer may depend on whether you think of the seasons in a more traditional, or a more weather-related way.

Astronomical Seasons Change at the Equinoxes and Solstices

The astronomical seasons are the ones most of us are familiar with because their start dates are listed on our calendars. They're called astronomical because, like our calendar, the dates of their occurrence are based on the position of Earth in relation to the sun.

In the Northern Hemisphere:

• Astronomical winter is a result of Earth's north pole being tilted its farthest away from the sun, and the sun's light aiming directly at southern latitudes. It begins on December 21-22. 
• Astronomical spring is a result of Earth's north pole tilt moving from its maximum lean away from the sun to one equidistant from the sun, and of the sun's light aiming directly at the equator. It begins on March 21-22. 
• Astronomical summer is a result of Earth being tilted its farthest towards the sun, and the sun's light aiming directly at north latitudes. It begins on June 20-21.
• Astronomical fall is a result of Earth's tilt moving from its maximum lean towards the sun to one equidistant from the sun, and of the sun's light aiming directly at the equator. It begins on September 21-22.

Meteorological Seasons Change Every 3 Months

Another way to define the seasons is by grouping the twelve calendar months into four 3-month periods based on similar temperatures.

In the Northern Hemisphere:

• Meteorological winter begins on December 1. It includes the months of December, January, and February (DJF)
• Meteorological spring begins on March 1 and includes the months of March, April, and May (MAM).
• Meteorological summer begins on June 1. It includes the months of June, July, and August (JJA).
• Meteorological fall begins on September 1 and includes the months of September, October, and November (SON).

Meteorologists didn't implement this classification just for the heck of it. Rather, they prefer to deal with data from whole rather than fractions of months, and align calendar dates more closely with the temperatures felt during that period, the scheme (which has been around since the early- to mid-1900s) allows weather scientists to more easily compare weather patterns from one season to another -- something the astronomical convention makes cumbersome due to seasonal lag (the delay in seasonal temperatures settling in).

Which Set of Seasons Wins Out?

The astronomical seasons are the more traditional way of defining our four seasons. Although folks may not be used to the meteorological way, in a lot of ways it's the more natural scheme for how we live our lives today. Gone are the days when we pore over the happenings of the celestial heavens and organize our lives accordingly. But organizing our lives around months and similar stretches of temperatures is more true to our modern reality.