Today is the day that the sun sets at exactly 7:00 PM from Washington DC. It also happens to be the day of the full "Harvest Moon" aka the full moon that occurs nearest to the fall equinox. This year's Harvest moon also happens (coincidentally) to be the "closest" full moon of the year because perigee also occurs within a few hours of the full phase, and this is the closest perigee of the year. As you can see on the Sky Almanac page, the full moon is listed as Sep 26 and perigee on Sep 27, but that just means that the moon reaches perigee after 0 hrs GMT tonight, so technically the date is the 27th.

So here is the science quiz question that I would like to pose... why does the sun set at 7 PM on Sep 26 instead of Sep 21 or Sep 23? I have already factored daylight savings time into the equation, in other words, sunrise would take place at 6 AM and sunset at 6 PM for exactly 12 hours of sunlight if daylight savings were not in effect.

Anyone know the answer? Try using the comment feature on this blog to take a guess.