Vince_Condella's Blog

The autumnal equinox occurs Monday at 10:44 a.m.  This is your second chance to welcome the new season of autumn.  Fall Part 1 took place on September 1 when we began meteorological autumn.  Yes, I know.  We meteorologists sure know how to confuse things.  But really, we just want to keep things simple.  So for the purpose of weather records, we consider the autumn season to be the months of September, October, and November inclusive.

The astronomers have other ideas.  The astronomical beginning of autumn occurs when the Sun is directly overhead at the equator.  This occurs twice a year - around March 22 for the vernal equinox (beginning of spring) and now.  At the time of the equinox (from the Latin for equal night), the hours of daylight and night are approximately equal.  On the equator they are 12 hours apiece.  For us, we will have a sunrise of 6:39 a.m. and a sunset of 6:48 p.m.  That equates to 12 hours and 9 minutes of daylight Monday.

The Earth is tilted on its axis by 23.5 degrees, so during the winter and summer solstice (first day of winter and summer), the Sun is directly overhead at 23.5 degrees south latitude or north latitude respectively.  If you can find a globe or a really good atlas, you may see something that sort of looks like a figure 8.  This is called an analemma.  It represents the path of the Sun over the Earth's surface, i.e. which latitude the Sun is directly overhead throughout the year. (see chart below)

Some people think it is all downhill from here.  Afterall, it gets to be a bit depressing when the Sun sets earlier and earlier each day, rising later and later each morning.  By the time of the winter solstice, our hours of daylight will have dwindled to a mere 9 hours.

But diminishing daylight also sets nature in motion.  I recently wrote about the flight of the Monarch butterfly to Mexico and its magical migration.  Other species begin to get moving when they perceive lesser daylight.  Even trees get into the act.  I'll have more about that in Monday's blog.