Winter solstice offers hope in our darkest hour

Ah, winter. Water dripping from a building rooftop in downtown Duluth grew into a shape resembling a perched bird this week. Credit: Bob King

The nights are long. You never seem to warm up. It must be winter. Or it will be anyway at 11:11 a.m. (CST) tomorrow Dec. 21 when the sun bottoms out in its yearly circuit of the sky like a cigarette crushed in an ashtray.

But every winter solstice has a silver lining; after tomorrow the sun begins moving northward again, chipping away at the darkness as it rises higher with each passing day.

Winter takes getting used to which is why we still call it fall in November and much of December. By the time the solstice rolls around on the 21st, we’ve long accepted the cold, snow and driving home at 5 with the headlights on.

The fundamental facts of life all revolve about the tilt of Earth’s axis. If our planet rotated straight up and down like Mercury, we’d have no seasons. Mid-latitudes would experience eternal spring with the sun forever stuck halfway between its summer high point and winter low. Some of you might like this … for a while.

The Earth’s tilt combined with its yearly revolution of the sun tip the northern hemisphere toward the sun in summer and away in winter. Credit: Tao’lunga / Wikipedia with my annotations

Meanwhile, those living at the equator would see the sun directly overhead at noon every day of the year, while  polar explorers and researchers would watch it skirt the horizon and never rise higher. For everyone the sun would rise and set at nearly the same time every day.

The sun’s noontime elevation changes from season to season thanks to the 23.5 tilt of the Earth’s axis. Stellarium

But no. The 23.5 degree tip of the Earth’s axis combined with our planet’s revolution around the sun break the monotony and create the seasons. The tilt ensures that the northern hemisphere of the planet nods toward the sun in summer and away in winter when we’re on the other end of our orbit.

Ethel O’Leary of Duluth deals with the consequences of Earth’s tilted axis as she clears the sidewalk in front of her house Dec. 5, 2013. Credit: Bob King

As a result of that nod, the sun appears high in the sky in summer. Its longer, steeper path across the sky means longer days and more intense heat. In the winter, the northern hemisphere “leans back” from the sun. Slanted, less intense solar rays and short days follow.

On Dec. 21 the sun reaches its lowest altitude above the southern horizon at noon for the year. Here in Duluth, that’s about 20 degrees or two fists held at arm’s length. For Chicagoans, it’s 25 degrees, a bit higher. But if you live in Anchorage, the solar disk climbs to just under 6 degrees before slinking back toward the southwestern horizon.

The sun’s path during the year hits a low in winter and a high in summer. Around the winter solstice, the sun travels little in the northward direction and appears to “stand still” in the sky. The same happens at the summer solstice. Come late January,the sun’s path is more steeply inclined to the horizon and it moves northward and higher in the sky. Longer days result. Credit: Dr. John Lucey, Durham University

Solstice literally means “sun stands still” and refers to the fact that around the solstice sunrise and sunset times change very little and the sun seems stuck in the same low spot in the sky. In December the sun sits at the “bottom” of its yearly path around the sky. Most of its daily motion is to the east and very little to the north. For the sun to get higher in the sky (and days to grow longer), it needs to spend more time moving “upward” or to the north. That starts happening in late January and accelerates during the spring when the sun’s path is more steeply angled to the horizon.

We’ve spent the last three months watching the sun glide to the cold bottom of the celestial sphere. Beginning tomorrow there’s nowhere to go but up. The next time you grab that snow shovel and heave a chunk of winter over the bank, know that the sun – starting tomorrow afternoon – will be on your side.

This entry was posted in Uncategorized and tagged , , , , by astrobob. Bookmark the permalink.
Avatar of astrobob

About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

12 thoughts on “Winter solstice offers hope in our darkest hour

      • Hi Bob;

        Ok, here’s a puzzler (for me). Looking at an analemma, I can picture the imaginary “figure 8″ drawn by the position of the sun at the same clock time from a fixed location on Earth over the course of a year. My question – why a figure 8? As the Earth travels faster in the winter and slower in the summer as it follows it’s elliptical orbit, why wouldn’t it simply trace an oval or egg shaped analemma in the sky? It seems to me that the Earth should consistently “under-rotate” relative to it’s faster rate of revolution in the winter and “over-rotate” relative to it’s slower rate of revolution in the summer. (I’m explaining this poorly but perhaps you can follow my logic that leads me to my question.)

        Jim

        • Hi Jim,
          Great question. The twist in the 8 just shows that both the sun’s location and the equation of time (sun “fast” or “slow” of the noon meridian) are equal in mid-April and late August. If you shot a photo showing the sun’s position at noon every day of the year, it would describe that figure 8 in the sky. Does this answer your question?

          • I’m getting really close to getting it. I’m trying to sort out if the “figure 8″ is all about axial tilt or if changes in orbital speed play a role. I think I’m pretty good at geometry, but this is complicated. Thanks for the response.

            Jim

          • Jim,
            It’s about axial tilt – that provides the vertical dimension of the 8 – and the elliptical orbit / variable velocity of Earth (side-to-side dimension).

  1. Thank you for this…the science and the hope.

    Here’s to another year! Please never stop posting. Happy Christmas and Merry Holidays!

  2. Hey Bob

    My grandfather used to have a shop in which he sold calendars, which show, for every day, the time of sunrise and sunset (for Brussels). He gave one to me every year since I was a little boy (in 1968), and I have bought one every year since he died. Every year in December these calendars had me wonder about the exact time of sunrise and sunset in the weeks before and after 21 December : while the sun is rising still a little bit later every morning, it is already setting a little bit later every evening. I have always wondered what might have the reason, and the only solution I could come up with was the movement of the earth in its path around the sun. And now, in your blog I read that that is exactly what it is : “In December the sun sits at the “bottom” of its yearly path around the sky. Most of its daily motion is to the east and very little to the north”. This eastward motion is what causes the sun to take a tiny bit more time the cross the horizon every day. The end result is that between December 17 and December 31, we win about 10 minutes of daylight in the evening, but still lose about 7 minutes in the morning. So after 40+ years of tearing away a page every day (with a joke on the back), my mystery has been solved.

    • Thanks for writing Jan. It’s a tricky thing to understand and visualize that’s for sure. Other factors involved in the sunset/sunset latest and earliest times involve Earth’s elliptical orbit and its changing orbital speed during the year.

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>