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Today brings the winter solstice and its brief nine hours and 15 minutes of daylight.
But the solstice — which marks the shortest day of the year, before the length of daylight starts to increase — doesn't really work on schedule here in Utah. So if your winter mornings seem extra dark even after the much-ballyhooed winter date arrives, there's a reason for that.
Mountains are a factor. The expectations are based on the supposition that east and west horizons are level, as if on a calm ocean. Not so in mountainous northern Utah.
Although the winter solstice is indeed today, the latest sunrise in Salt Lake City will be Dec. 31, when old Sol will peep over the horizon at 7:51 a.m. That's four minutes later than on the official winter solstice.
Sunrise actually doesn't get earlier in Salt Lake City until Jan. 9 — the true "turn-around day" — when it moves back to 7:51 a.m.
The U.S. Naval Observatory Web site explains why mid-northern altitudes such as northern Utah qualify for what could be called "The Dark Days of Winter."
However, Patrick Wiggins, NASA solar system ambassador to Utah, said it's the "why" that is tricky. "It's a lot like understanding the theory of relativity."
"The period between the first week in December and the first week in January could well be called the 'dark days' for the mid-northern latitudes. At latitude 40 degrees north (Salt Lake is latitude 40.8 degrees north) earliest sunset occurs around Dec. 8 each year, and latest sunrise occurs around Jan. 5," the Naval Web site states.
It was the sense among ancient people that the sun was gong away entirely that led to the use of fires and lights in late December to try to coax it back, a practice that invariably worked as days gradually got longer. The custom hangs on in many modern Christmas traditions.
Modern time zones and 24-hour timekeeping systems apparently complicate things, as does the tilt of the earth in relation to the sun, which is what gives the Earth its seasons.
Even nearby Logan and St. George differ from Salt Lake City because of slight differences in latitude and longitude.
Today, St. George has a sunrise four minutes earlier than Salt Lake City and a sunset that is 18 minutes later. In Logan, sunrise is three minutes later than Salt Lake City, while the sunset is three minutes earlier today.
The summer solstice and the longest day of the year has the same out-of-sync effects in northern Utah, but in reverse.
"A similar situation occurs at the summer solstice (usually June 21), although the effect is not as extreme ... ," the Naval Web site explains. "At latitude 40 degrees north the earliest sunrise occurs around 14 June and the latest sunset around 28 June."
Salt Lake City's longest day is June 21 — with 15 hours and six minutes of daylight — but the earliest sunrise for the year is 5:56 a.m. MDT, which is true from June 7-June 22.
The latest annual sunset in Salt Lake City is 9:03 p.m. MDT, which happens daily from June 23-July 2.
Go the the Navy's Web site, aa.usno.navy.mil/data/docs/RS_OneDay.html, to find sunrise and sunset times for any location.
For information on past and future solstices and equinoxes see Wiggins' Solar System Ambassador's Web site at utahastro.info/.
E-mail: lynn@desnews.com