HAIL TO THE CHIEF: What You May Not Know About The Equinox
For the past several days you’ve been hearing about the Autumnal Equinox beginning at 9:29pm Central Time in the Quad Cities. You might have learned that from pole to pole on our planet an ‘equal’ amount of daylight and nightlight takes over, right? Well, lets check out Monday’s sunrise and sunset:
SUNRISE: 6:49am; SUNSET: 6:59pm.
If you add it up that is 12 hours and 10 minutes of sunlight. Well, let check the next day, Tuesday since that will be the first full day of autumn:
SUNRISE: 6:51am; SUNSET: 6:57pm. Hmmm. In fact, the closest we see 12 hours of daylight and nightlight will be on Thursday, September 25th where the sun will rise at 6:53am and set at 6:54pm. So, what gives?
It has to do with the earth’s atmosphere and how it affects the appearance and apparent position of any celestial object. In this case the sun.
Its all based on REFRACTION. If we had no atmosphere on this day, then the sun would be below the horizon as we see at position A. However, with the aid of the atmosphere refraction causes the sun’s rays to bend down toward the observer so that appears to be at position B. This delays sunset by several minutes. Higher latitudes experience close to 20 minutes of added light on this day.
Refraction also causes the sun to appear more squashed than round either at sunset or sunrise.