Not So Fast, Summer

It’s a pleasant day in central Virginia. At 3 PM the temperature is 76°F (24.4°C) and the humidity is low: only 34%. I have a front window open and a back door open, and the gentle breeze feels good. I’m feeling expansive, which can only mean, dear readers, that the time has come once again for me to impart some of my fantastic wisdom into your puny brains. No, wait. That isn’t right. I meant to say, it’s time to impart some of my puny wisdom into your vast intellects. Nah. That doesn’t sound right either. Let’s just get on with it.

Today is the last official day of summer for 2014 for the northern hemisphere (last day of winter for the southern hemisphere). In the northern hemisphere, the autumnal equinox will occur today (Monday) at 10:29 PM EDT (Eastern Daylight Time). Alternately, I could say the equinox will occur on Tuesday, September 23, at 02:29 UTC (Coordinated Universal Time). Yes, folks, it will be both Monday and Tuesday at the same time – just not in the same place.

What is an equinox, anyway? It is a point in the earth’s orbit around the sun at which every place on the earth experiences equal parts daytime and nighttime. This happens twice for each trip around the sun. It happens in March and again in September. The date and time of the equinox is calculated by astronomers, and in their calculations they assume the earth is a perfect sphere. But it isn’t. It’s slightly bigger at the equator than at the poles. And different places on the earth’s surface are at different elevations above sea level. These factors mean that the autumnal equinox will occur at slightly different times for different places. (If you live exactly on the equator, then you’ll receive exactly 12 hours of daylight every day of the year.)

So, of course, I began to question when the autumnal equinox will occur for my city. For the answer, I went to the U.S. Naval Observatory website. It has a handy calculator for determining time of day for sunrise and sunset almost anywhere on the earth. The calculator produced a calendar for 2014, and a quick review of September showed that the 25th had 12 hours and 2 minutes of daylight in my city (more day than night), while the 26th had 11 hours and 59 minutes of daylight (less day than night). Clearly, the local equinox must occur sometime during one of those days: either the 25th or the 26th.

For you, dear readers, tomorrow may be the first day of fall. For me, tomorrow – and the day after – will belong to summer. I will await them, watermelon martini in hand, refusing to acknowledge the waning of the light.