The Wanderings of the Arctic Circle
The Milankovitch Cycle
Article #1349, August 7, 1997
This article is by Ned Rozell, a science writer at the Geophysical Geophysical
Institute, University of Alaska Fairbanks, in cooperation with the
UAF research community, and was provided as a public service. Ned Rozell was hiking the trans-Alaska pipeline
that summer to
commemorate the 20th anniversary of the Alaska Science Forum and the
"After 506 miles of walking, my dog Jane and I just hiked over the
dashed line that encircles the top of every globe-the Arctic Circle.
I'd like to pitch the tent precisely on the Arctic Circle, but it's
not easy to pinpoint because the imaginary line is almost constantly
on the move.
"The Arctic Circle is known to most people as the spot where the
sun never sets on June 21, the summer solstice, and the spot where
the sun never rises on December 21, the winter solstice. The
movement of the Arctic Circle due to changes in Earth's axis is
called the Milankovitch Cycle, which was named for Serbian
climatologist Milutan Milankovitch.
"Milankovitch recognized that the tilt of Earth's axis shifted
from about 22 to 24.5 degrees every 20,000 years. Then, he observed,
the axis shifts back in another 20,000 years. Geophysical Institute
Professor Emeritus Tom Hallinan said Earth is sort of like a
spinning top that has a little bit of wobble. That wobble is what
happens during the Milankovitch Cycle.
"How does the wobble affect the Arctic Circle? The 2.5 degrees of
axis shift every 41,000 years equals about 200 miles of movement in
that time, or about 25 feet each year. T. Neil Davis, who wrote the
Alaska Science Forum column 20 years ago, pointed out that the
wandering of the Arctic Circle is highly variable. The circle's
location may change as much as 50 feet every year, making it
difficult to be a perfectionist when posing for pictures at the
Arctic Circle wayside on the Dalton Highway, or when pitching one's