A voice on the radio the other day told me we’d be welcoming in “meteorological autumn” on the first day of September. Our calendar shows Sept. 22 as first day of the new season. Does autumn really not begin until the third week of September? Does anyone care? These are questions that beg for answers. First, a definition.

Bob Kalish observes life from a placid place on the island of Arrowsic (motto: You’re not in Georgetown yet). You can reach him at [email protected]

The National Geographic Society defines a season as a period of the year that is “distinguished by special climate conditions.” The four seasons – spring, summer, fall and winter – follow one another regularly and each has its own light, temperature and weather patterns that repeat annually.

In the Northern Hemisphere, astronomical winter (defined by the apparent movement of the sun and stars) generally begins on Dec. 21 or 22, when the winter solstice marks the date the sun is lowest in the sky, the day of the year with the shortest period of daylight. Astronomically, summer begins on June 20 or 21, the summer solstice, the longest day of the year. Spring and autumn begin on days that have equal amounts of daylight and darkness (called equinox) because the sun is directly over the equator. The vernal, or spring, equinox falls on March 20 or 21, and the autumnal equinox is on Sept. 22 or 23, days that have equal amounts of daylight and darkness. Seasons occur as they do because Earth is tilted on its axis and wobbles and that’s enough. Winter typically has cold weather, little daylight and limited plant growth. In spring, plants sprout, tree leaves unfurl and flowers blossom. Summer is the warmest time of the year and has the most daylight, so plants grow quickly. In autumn, temperatures drop and many trees lose their leaves.

The seasons in the Northern Hemisphere are the opposite of those in the Southern Hemisphere. This means that in Argentina and Australia, winter begins in June and Santa Claus wears swim trunks. The winter solstice in the Southern Hemisphere is June 20 or 21, while the summer solstice, the longest day of the year, is Dec. 21 or 22. Confusing, no?

Now these labels apply to physical events. But when railroads carved up time zones to make it easier to travel, it was easiest to have time zones congruent with the local time zones and comfortably within the arbitrary borders of the time zones. Thus the “astronomical” dates for the change of seasons is still tied to the actual movement of the sun and stars, whereas the meteorological definition is linked to the calendar.

What is really interesting is how it all comes down to an error in design. You see, the seasons exist because the Earth wobbles on its axis. Other planets don’t wobble and so they have no seasonal differences and they can receive cable television without a cable. But Earth, because of its wobble, supports life – if that’s what you call it.

Comments are not available on this story.

filed under: