Just a few days ago, this past Tuesday, at 5:18 PM eastern time, Summer 2009 ended and Fall 2009 began.

The sun was heading back south from the northern hemisphere and sitting directly over the equator. The sun sits directly over the equator twice a year, usually around March 21st (signaling the start of Spring - also known as the Vernal Equinox), and again in mid September.  As many of us learned years ago, the "equinox" means an "equal amount of day and night" on that particular day... OR does it?

The fact is, the days are NOT equal day and night on either the Spring (Vernal) or Autumnal Equinox. In fact, checking the official sunrise and sunset tables for this past Tuesday's equinox, the sun rose at 6:52 AM and it set at 7:02 PM. A little math tells us that comes out to 12 hours and 10 minutes of daylight on the equinox. So that begs the question "what's up with that?"

Here's what's up with that: The reason the sunrise and sunset don't match the equinox date is because of refracted and reflected sunlight. Simply put, the sun actually rises several minutes later than it seems and actually sets several minutes sooner than it seems. In the morning, the sun's light shines above the horizon earlier than the actual sunrise as light is reflected and refracted off the atmosphere BEFORE the disc actually reaches the horizon, This accounts for several minutes difference right there. Then, at sunset, the sun actually goes down over the western horizon several minutes SOONER than it seems to us as light continues to be reflected and refracted back AFTER the disc has already dropped below the horizon line. To the human eye, on both the sunrise and sunset, we see the sun's light, in the shape of a disc, and believe that is the ACTUAL disc of the sun, but it's not. It's merely the suns light reflected and refracted off of the atmosphere.

Most sunrise and sunset tables don't take into consideration any time differences related to reflected or refracted sunlight, and thus, typically the amount of day and night we use for an equinox day is seemingly not equal. We usually have to wait another two or three days to make up that 5-10 minutes difference and finally have our sunrise and sunset tables appear to be correct.

As broadcasting legend Paul Harvey used to say, "And now you know the rest of the story!"