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The science of winter solsticeAt 8:30 p.m. Alaska Standard Time on Dec. 21, take a deep breath. That is the precise moment of winter solstice. You will be more than four hours into the longest night of the year, said to be 18 hour and 33 minutes long in Anchorage by the U.S. Naval Observatory. The sun won’t rise for another 13 hours and 30 minutes. In astronomical terms, winter solstice in the northern hemisphere isn’t a day but an instant — the very moment that the Earth’s axial tilt has leaned the geographic North Pole farthest away from the Sun. This seasonal reach toward the cold abyss of space and away from the solar furnace — the source of our seasons, and the cause of our long winter nights — climaxes when we reach 23 degrees and 26 minutes off plumb, sometime on the Solstice Day. Here’s what the Earth looks like right now. On Dec. 21, Anchorage sunrise occurs at 10:14 a.m. with sunset following five hours and 27 minutes later at 3:41 p.m., says the U.S. Naval Observatory calculator for sunrist and sunset times. But we quickly start to lean back. As the home planet spins three more times, we will travel along the orbit to a position where the tilt has eased just a bit. By Christmas, we will have gained two minutes of possible direct sunlight, and it accelerates from there. More than other states, Alaska celebrates summer and winter solstices with gusto. This week’s version may mean a ski by moonlight in Russian Jack Park, or a few hours in an outdoor hot tub staring at the stars. For those who prefer a bit of company, here are a few celebrations: Homer -- Center for Alaskan Coastal Studies hosts a moonlight family snowshoe at the Carl Wynn Nature Center 6-9 p.m. Wednesday. Snowshoes can be rented and a bonfire will roar. Hot chocolate will be served. Call 907-235-6667 for information. Anchorage - Winter Solstice Torchlight Skating Party, 6-8 p.m. Thursday at the Cuddy Midtown Park Skating Oval. Music, a bonfire and ice skating highlights the gathering hosted by Anchorage Skates, which reports on its website: “The warm winds and melting and refreezing have smoothed out the ice. It’s as good as it’s been so far this Chinooky year.” Alaska Mountaineering and Hiking will offer demonstration speed skates and light tiki torches. Non-skaters are asked to park at the far back (southwest corner) of the Loussac Library lot. Another outdoor gathering is 7-9:30 p.m. Wednesday at the McHugh Creek Trailhead. The Anchorage Adventurers Meetup Group will gather with warm drinks and snacks about 100 yards up the hill from the lower parking lot. Because of limited parking, car-pooling is required. Eagle River -- The Eagle River Nature Center decorates with ice lanterns during its annual Lantern Walk and Solstice Celebration on Dec. 17th. There will be a bonfire and participants should bring a dessert for the end of the walk. Free program, but $5 parking for non-members. Call 907-694-2108 for more information. In Fairbanks -- Fairbanks Community Museum will celebrate noon to 8 p.m. Wednesday with hot cocoa served all day. There’s also a special holiday art show commemorating the history of Fairbanks through watercolor. Call 907-457-3669 for information. Contrary to popular belief, the tilt of the earth does not, as stated in this article, "climax" at an angle of about 23 degrees on solstice day, and then "quickly start to lean back." While it is true that the axial tilt of the earth changes, it does not change annually as stated above. There is a cycle of oscillation whereby the earth's angle of tilt (obliquity) varies from about 21 degrees to about 25 degrees, but this only happens over the course of about 41,000 years. Additionally, there is cycle of precession that spans about 21,000 years. But there is no annual tilt cycle that is responsible for the seasonal changes in climate or daylight. So what does cause the days to get shorter and colder? The simple answer is that as the earth makes its annual trip around the sun, during summer the tilt is pointed more towards the sun, and during the winter it is pointed more away from the sun. But the tilt itself remains essentially unchanged. Correct, kenryan. Our seasons are caused by the fact the plane of the earth's orbit is not 90 degrees from the orientation of its poles. If the earth was more "upright," the only seasonal changes we would see would be a slight warming what we consider to be the northern winter and cooling in the summer, due to the fact the earth is closest to the sun in December - February. We would probably have to rename the seasons, and the southern hemisphere would have the exact same seasons as we do, i.e. it would be "summer" in January everywhere on earth. Furthermore, the article errs in stating that the progression in day length is quick at/around the solstice. In fact, the word solstice is based on the Latin for the sun (appearing to) stand still over several days. A graphic depiction of day length versus day of the year takes the shape of a sine wave, with peaks and troughs being the summer and winter solstices. The rate of chage of the curve at these points is at a minimum compared with the steep curve at the equinoxes. We lost only nine seconds of daylight today. On the spring and fall solstices our daylength changes by around 340 seconds per day. It will take a week for us to gain back only a few minutes at this time of year. A week at the equinoxes yields close to 45 minutes of change. Too bad our science education is so mediocre that the average journalist lacks the ability to understand what he/she is writing about. I bet the same mistakes would not be made in reporting on pop culture or fashion "facts." |
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