The Earliest Sunset of the Year

I'm guessing that most of you, after reading the title, would guess that this event will occur on the winter solstice, typically December 21st.  But it's a strange little quirk that while the winter solstice is the shortest day of the year, it doesn't have the earliest sunset (or latest sunrise).  The reasons get pretty technical and probably not of much interest to most (see this link for more info).  They include that:

  • A day is technically not exactly 24 hours long.
  • The earth is not an exact sphere.
  • Sunrise and sunset are measured by the top of the solar sphere and the horizon, not the center of the solar sphere.
In any event, the date of the earliest sunset is actually determined by latitude (i.e. how far you are between the earth's equator and the pole).  This figure from Stephan Aman shows this nicely.  So if you think it's strange to have our earliest sunset 10 days before the shortest day of the year, think about how folks in Key West, FL feel, where their earliest sunset is just after Thanksgiving.


Thus if you're not a fan of the short days of winter, you can comfort yourself in the fact that the sunsets will be fractionally getting later each day starting tomorrow.

TimeandDate.com has a nice table that shows all of this as well.  Note that our sunrise time continues to get later faster than our sunsets after today, so the length of the day is still getting shorter until December 22nd.


But there's something else that's a little peculiar and unique to our corner of the country, and this was pointed out by Dr. Brian Brettschneider, the state climatologist for Alaska. He created a map of all of the earliest sunset times.


It's a pretty crazy map, I know.  It has to do with the fact that the time zones come into play.  If you live on the eastern side of a time zone (like Kellogg, ID), sunset will be earlier than the western side of the time zone (like Seattle).  And also, our time zones are not perfect north-south lines, for mostly geopolitical boundaries (e.g. states, counties, media markets, etc.).

But take a look at the 3:30 to 4:00 pm (orange color) area on the map in the lower 48 states.  You'll notice that the only places that have a sunset before 4:00 pm are the Idaho Panhandle, northeast Washington, and much of Maine.  That's kind of strange when you think about it.  Nearly everyone in the US has a sunset that is always later than 4:00pm.  Even Wenatchee and the Tri-Cities.  


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