Wednesday, November 11, 2009

Sunrise and sunset vs. shortest day of the year

At mid-latitudes on the earth, like in Utah, sunrise and sunset both don't automatically turn around on Dec. 21, the so-called year's shortest day.
The latest ever sunrise in Salt Lake City is 5:01 p.m. That occurs on Dec. 14-17. By Dec. 18, sunrise has moved back a minute to 5:02 and sunset is 5:03 on Dec. 21.
The shortest day in S.L. is actually plural -- only 9 hours and 15 minutes of daylight, from Dec. 20-25 -- a six-day span.
What about sunrise?
Sunrise is 7:48 a.m. in Salt Lake on Dec. 21. However, it moves to 7:49 -- even later on Dec. 22.
Sunrise in S.L. gets stuck at its latest ever time --7:51 a.m., from Dec., 27-Januay 8. It is not until January 9 when sunrise starts to get earlier again in S.L. -- at 7:50 a.m.
Now realize that ALL sunrise/sunset times you see quoted here or anywhere are based on a hypothetical LEVEL, FLAT horizon. There is NO allowance for mountains or hills.
As far as sunset goes, June 23-July 2 features Salt Lake's latest ever sunset -- stuck at 9:03 p.m.
Salt Lake's longest day of the year, is actually a few "days," around June 21, with 15 hours and 6 minutes of daylight.
Salt Lake's earliest ever sunrise is between June 7-June 22, when it is stuck at 5:56 a.m. MDT.
Logan, St. George and even Ogden would be slightly different on all these times.

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