Screen Name Required

      A screen name is required for sharing content on REI. Click here to create a screen name before continuing.

      Set screen name

      Have You Noticed Sunset Times Rarely Change Lately? What's Up with Sundown?

      How much daylight will your patch of the planet receive on Thursday, Dec. 22, the date of the 2011 winter solstice?

      And while no day is shorter than Thursday, why is it that sunset times have hardly budged since early December?

      First, here's how much time the sun will spend above the horizon on Thursday in 25 randomly selected cities where REI operates stores: 

      City Daylight on Dec. 22
      Houston     10h 14m 02s
      Austin, Tex.     10h 11m 33s
      Tucson     10h 02m 16s
      Chula Vista, Calif.     10h 00m 17s
      Atlanta       9h 54m 30s
      Santa Barbara, Calif.       9h 51m 09s
      Greensboro, N.C.       9h 42m 28s
      Las Vegas       9h 41m 50s
      Richmond, Va.       9h 34m 13s
      San Francisco       9h 32m 54s
      St. Louis       9h 27m 41s
      Reno, Nev.       9h 22m 37s
      Denver       9h 21m 23s
      Pittsburgh       9h 16m 58s
      Salt Lake City       9h 14m 53s
      New York City       9h 12m 28s
      West Hartford, Conn.       9h 08m 28s
      Ann Arbor, Mich.       9h 05m 10s
      Boston       9h 04m 50s
      Madison, Wisc.       8h 59m 38s
      Boise, Idaho       8h 55m 57s
      Bloomington, Minn.       8h 46m 09s
      Portland, Ore.       8h 42m 06s
      Seattle       8h 25m 17s
      Anchorage (Dec. 21)       5h 27m 00s

      Source: Timeanddate.com, sunrise and sunset calculator. Note: The 2011 winter solstice occurs at approximately 12:30 a.m. EST on Dec. 22 (9:30 p.m. PST, Dec. 21).

      But what about those strangely stagnant sunset times? Here in Seattle, REI's home turf, the year's earliest sunset, 4:18 p.m., first occurred on Dec. 5. (Yep, we know, we know; 4:18 p.m. is mighty early for a sunset.) Through Dec. 16, that time never changed. Since then sunset times have actually occurred later. On Dec. 22, the sun will set at 4:21 p.m.

      Even so, all that time the sun has been rising later and later. It came up at 7:41 a.m. on Dec. 5, but on Thursday it won't rise until 7:55 a.m.

      Big Bend NPMove closer to the equator and the same pattern is found. On Dec. 1 in Houston, for example, sunset occurred occurred at 5:22 p.m. On Thursday it occurs 5 minutes later. Yet the sun will rise 14 minutes later than it did on Dec. 1.

      Why is this? Two factors:

      • Earth's elliptical orbit. A difference exists between "solar noon" (aka "local noon"), the time each day the run reaches its highest point in the sky, and what we nonastronmers call straight-up high noon (when our clocks show 12:00). In Seattle, solar noon happens on Dec. 22 at 12:08 p.m.; in Houston, 12:20 p.m. Because the earth travels in an elliptical orbit, not a circular pattern, solar noon occurs later in the day between October and April.

      The tilt (23.5 degrees) of the earth's axis. The North Pole will be as far from the sun as it gets on Thursday. While solar noon grows later, this gradual, progressive tilting of the earth's axis through the solstice time frame keeps the sunset times in place. Meanwhile, sunrise times occur later and later. The latest sunrise time in Seattle, for example, is 7:58 a.m. (Dec. 30-Jan. 4). Yet by Jan. 4, though, sunset will occur at 4:31 p.m., and the amount of daylight will have expanded by more than 8 minutes.

      Explanations for this phenomenon are offered in an academic overview from Cornell University's Ask an Astronomer service, from earthsky.org, and in an article published in The Seattle Times.

      However the planet does it, I'm just happy to know daylight hours will soon be back on the increase. The payoff here in the Northwest comes in early summer, when evening afterglow lingers long in the high country. So even if I stretch a hike later than wisdom dictates (standard procedure for me), I can usually keep your headlamp tucked away until 10 p.m. Good times. C'mon, summertime.

      Photo above: Ocotillo silhouetted by a sunset at Big Bend National Park in Texas, by Jack Hamann. Below: Sunset at Zion National Park by REI's T.D. Wood.

      Posted on at 1:25 PM

      Tagged: Solstice, solar noon, sunrise and sunset

      Ratings and Comments

      (0) (0)
      write a comment
      You already voted on this.
      Log in to comment or rate.
      Gearhound99

      When I lived in Alaska, I finally grasped the concept that every place on the planet gets the same amount of daylight in a year..it's only how it's spread around that varies. The Anchorage Daily News used to have a handy box on the top of the front page every day the showed SR/SS, the length of the day, and the number of minutes gained/lost.

      Flag as Inappropriate

      Flagging Questionable Content Protects the Community at REI.com

      In what way this content is inappropriate? Please check one:

      More Details (Optional)

      Submit answer

      Reply
      JonSills

      Earth's axial tilt - it's the reason for the season! :)

      Reply

      Unable to Post Comment

      We were unable to post your comment at this time. Your opinion matters, so please try again later.

      Close
      • Most Recent
      • Most Commented

        No entries found

        No entries found