Does it seem like your winter mornings are extra dark even after the much-ballyhooed winter solstice?
There's a reason for that.
Although the winter solstice is indeed on Dec. 21 as advertised, that is NOT the day for the latest sunrise in Salt Lake City. The sunrise in Salt Lake City is at 7:48 a.m. Dec. 21. However, it will be at 7:49 a.m. on Dec. 22; moves to 7:50 on Dec. 24; and to 7:51 on Dec. 27.
By Dec. 31, Salt Lake's sunrise is 7:52 a.m. — its latest of the year and four minutes later than on the winter solstice.
Sunrise doesn't get earlier in Salt Lake until Jan. 9 — the true "turn-around day" — when it moves back to 7:51 a.m.
Dec. 21 is indeed the shortest day in Salt Lake City, with only 9 hours and 15 minutes of daylight. By the time of the winter solstice, the sun has already reached its earliest setting, but dawn at this latitude is a little slower, and the sun has not reached its latest rising.
For example, sunset is actually at 5:03 p.m. on Dec. 21 in Salt Lake City. But it was 5:02 on Dec. 19 and 5:01 on Dec. 14. Sunset is at its earliest in the Salt Lake area Dec. 2-Dec. 13, locked in at 5 p.m., an appointment its keeps for 12 consecutive days. Dec. 14 marks the "turn-around" day for sunset — not Dec. 21.
(Our sunrise and sunset times don't actually agree with reality, either. They are figured as if the east and west horizons were level — as if on a calm ocean. Thus, mountains delay the true sunrise and/or sunset here.)
This is all according to the U.S. Naval Observatory Web site.
The Web site's FAQ section explains why mid-northern altitudes — like northern Utah — qualify for what could be called "The Dark Days of Winter."
However, Patrick Wiggins, NASA solar system ambassador to Utah, said the "why" that is so is very complicated and he said "It's a lot like understanding the theory of relativity."
He also said he's always been afraid someone would ask him this question one day and that some days he's not sure he fully understands the "why" to this tricky phenomenon. It's a quirk of Utah's latitude — in most, the winter solstice is everything we thought it was.
"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 8 December each year, and latest sunrise occurs around 5 January," The Naval Web site states.
"The day with the least amount of daylight is the winter solstice, the first day of winter, around 21 December. Why are not all these dates the same? The answer is not simple. There are two effects which, together, determine the local time of sun phenomena, such as sunrise, sunset, and transit. One is the called the Equation of Time, the other is the sun's declination," it states.
Our time zones and 24-hour timekeeping apparently complicate things, as does the title of the earth in relation to the sun, which is what gives our planet its seasons.
Where you go on earth obviously changes sunrise and sunset times. Even nearby Logan and St. George differ from Salt Lake City , because of their slight differences in latitude and longitude.
For example, on Dec. 21, St. George has a sunrise four minutes earlier than Salt Lake and a sunset that is 18 minutes later. In Logan, sunrise is three minutes later than Salt Lake city, while the sunset three minutes earlier on Dec. 21.
What about June 21 in Salt Lake, the summer solstice and the longest day of the year?
"A similar situation occurs at the summer solstice, although the effect is not as extreme," The Naval Web site explains. "Solstice occurs around 21 June, but at latitude 40 degrees north the earliest sunrise occurs around 14 June and the latest sunset around 28 June. "
As expected, Salt Lake's longest day is June 21 — with 15 hours and six minutes of daylight — but the earliest ever sunrise for the year is 5:56 a.m. MDT, which is true (rounded off) from June 7-June 22.
The latest annual sunset in Salt Lake is 9:03 p.m. and that happens daily from June 23-July 2.
According Wiggins, winter (by astronomical definitions) officially starts for Salt Lake City at 5:22 p.m. MST, on Thursday, Dec. 21, when the sun reaches its most southerly point in our skies of our northern hemisphere.
Following this event, known to astronomers as the December solstice, the sun will seem to start creeping back to the north and the periods of daylight will gradually grow longer and warmer.
Things are reversed in the southern hemisphere where the December solstice is seen as the beginning of summer.
Many of the holiday traditions we enjoy at this time of year originated in ancient solstice ceremonies.
"An example of this is our use of holiday lights." says Wiggins. "In ancient times people kept a very close eye on the sun at this time of year since everyone could see that it was getting lower in the sky each day. They feared that if something wasn't done, the sun would soon disappear altogether.
"So the worried people built great bonfires to entice the sun to stick around and, sure enough, every year their efforts paid off and the sun reversed course and started its gradual climb higher and higher into the sky," Wiggins said.
Go the the Navy's Web site, aa.usno.navy.mil/data/docs/RS_OneDay.html to find sunrise and sunset times for anywhere, plus a detailed explanation of this special effect for mid-northern latitudes, like Salt Lake.
For information on past and future solstices and equinoxes see Patrick Wiggins' Solar System Ambassador's web site at: utahastro.info.