Winter solstice ushers in more daylight

While there is more darkness than daylight this time of year, the numbers will start to reverse on Tuesday with the arrival of the winter solstice. The days will become longer, the nights shorter and the sun higher in the sky.

The winter solstice occurs on December 21 at 4:38 p.m. Pacific Time, when the North Pole is at its farthest point from the sun. The earth is tilted at 23.5 degrees and on the winter solstice, the North Pole is tilted away from the sun while the South Pole is tilted towards the sun. The sun will be directly overhead at the Tropic of Capricorn.

The sun’s low position in the sky is definitely noticeable this time of year with the long shadows, late sunrises and early sunsets. The sun will be at its lowest position in the sky relative to the horizon on the winter solstice. However, the latest sunrise and the earliest sunset do not occur on the solstice.

In Bonners Ferry, the latest sunrise will be at 7:38 a.m. on December 27 through January 5, while the earliest sunset was at 3:49 p.m. on December 8 through December 14. Due to the surrounding mountains, our local sunrise and sunset are later and earlier, respectively. 

Regardless of terrain, the length of civil twilight is approximately the same. Civil twilight is when the sun is between the horizon and six degrees below the horizon either before sunrise or after sunset. In more usable terms, civil twilight is when terrestrial objects, such as mountains, can be clearly distinguished by twilight illumination.

On the winter solstice, civil twilight will start 37 minutes before sunrise and end 37 minutes after sunset. Between December 20-23, the least amount of daylight shines on Bonners Ferry at 8 hours and 16 minutes, with 1 hour and 14 minutes of civil twilight and 14 hours and 30 minutes of darkness.

Eight hours of daylight is fairly reasonable compared to Alaska. In Anchorage, their shortest amount of daylight is about 5.5 hours, while Fairbanks is 3 hours and 43 minutes.

Barrow, the northernmost city in the United States, is the darkest in Alaska. At 330 miles north of the Arctic Circle, the sun sets on November 19 and does not rise again until January 23. They are not in complete darkness due to civil twilight. Civil twilight decreases until winter solstice when it reaches a minimum of three hours.

While winter may seem long, it is actually the shortest season. Interestingly, not all the seasons are the same length because the earth doesn’t move at a constant speed in orbit. Winter, from the winter solstice to the spring equinox, is only 89.0 days long. Spring is 92.8 days and autumn is 89.8 days. Our longest season is summer at 93.6 days.

As winter begins, the increase in daylight will be minimal at first, but by the end of December we will have gained five minutes of daylight. This year, the longest nights will be illuminated by a full moon, which coincides with the winter solstice.