For those of you keeping score at home, a change in seasons is almost upon us, as the first equinox of 2008 occurs on Mar. 20 (or Mar. 19, if you're in the Mountain time zone or westward of this longitudinal marker). In the Northern hemisphere, this heralds the official start of spring, whilst antipodeans in the Southern hemisphere get started with autumn. You'll be pardoned, of course, for the traditional frustration if the actual weather outside your door pays absolutely no heed to the official seasonal shift.
This isn't a surprise, since the equinox has been a misnomer almost from the coining of the term. The etymology of equinox is Latin, from aequus, meaning equal, and nox, for night. Ostensibly, the word refers to a date when day and night are both precisely the same length, but on the equinox, the actual day is longer than the night. For that, you can blame astronomers.
One of the common astronomic connotations of equinox is a day where the sun spends an equal amount of time above and below the horizon. However, astronomers make these determinations from the center of the sun's visible disc, so even when the sun is "below" the horizon, a portion of its disc is still showing. On average, this makes the day 14 minutes longer than the night on the date of the equinox.
In strict astronomy terms, the equinox occurs when the sun directly aligns with the point in space where the Earth's equator lines up with the ecliptic plane of the solar system. As most of us learned in elementary school, the Earth tilts on its axis — about 23.5 degrees — so that the equator is never "flat" with the ecliptic. It is this tilt, and the fact that the Northern and Southern hemispheres incline closer or farther away from the sun as the Earth completes its yearly orbit, that create our seasons.
For those of us in the Northern hemisphere impatient with the meteorological arrival of spring lagging too far behind the scheduled arrival of spring, be thankful you don't reside on one of the other local planets — some of which sport far more unforgiving axial tilts and seasonal variations. One planet in particular has an inclination so extreme, its winters are measured not in months or years, but decades.
WHAT PLANET IN OUR SOLAR SYSTEM HAS THE HARSHEST WINTER?Get the answer.
Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can also follow him on his personal blog.