Monday, December 7, 2009

Welcome to the earliest sunset of the year

Although there is no doubt that the day with the least total amount of daylight is December 21st (the winter solstice), the earliest sunset of the year actually occurs on December 8th.

The reason has to do with something called the Equation of Time and depends on the tilt of the earth and the shape of its orbit around the sun. You can read the detailed explanation of why here.

Although the time the sun sets will be getting later from now on until the summer, the sunrise will continue to be later and later until early January. Also remember that at this time of the year there is usually only a few seconds to a minute difference between the sunrise and sunset times from day to day. So by the end of the month the sunset will only be about 10 minutes later than it is today.


Anonymous said...

Sorry, this isn't to do with your original post, BUT, is the rain gauge having issues on the UWWS? The reason I ask is because I thought I saw a number somewhere in the 26ish mm early yesterday morning, but it had changed down to 15.6mm yesterday by the afternoon, and it has stayed there even though we've been getting rain and/or snow pretty much since yesterday at midnight. ???

Frank said...

You are correct that the total precipitation changed during the day.

The reason was that we are in the transition between using the tipping bucket rain gauge (that can only measure liquid precipitation) and the GEONOR gauge (that measures total precipitation).

At this time of year it gets difficult to decide whether or not the precipitation is frozen or liquid and thus which gauge results to show. For the rest of the winter we will probably be showing the readings from the total precipitation gauge.