2008 Blog Archive

Check Back Daily December 2, 2009, South Pole Station
Hermann Kolanoski

Editor's Note: To see Hermann's neat pictures of IceCube/IceTop, visit this Web page.

How did Amundsen and Scott know they were at the South Pole?

Amundsen and Scott could not exploit modern navigational tools, like radio navigation or GPS. Even worse, in the austral summer in Antarctica you cannot use the sailor's traditional method of celestial navigation because it’s always daylight. You only see the sun and that the whole day long.

The North and South Poles are defined as the two points on the Earth's surface through which the Earth's rotation axis passes. Since the Earth's axis does not change its orientation relative to the plane in which the Earth circles around the sun, the two poles are the only locations on the planet where you see the sun under the same angle relative to the horizon for the whole day. That was basically the principle by which the discoverers found the South Pole.

Their measurements must have been sufficiently precise because Robert Scott obviously found without problems the tent with the flag which Roald Amundsen left there to mark the Norwegian team's arrival as the first to reach the Pole. Amundsen actually stayed several days at the South Pole to check over a longer period that the angle to the sun did not change. On my way to Antarctica, I saw in the Antarctic section of the museum in Christchurch the sextant and theodolites which the South Pole expeditions used for navigation (see picture).


Left: The Scott Party at the South Pole in January 1912 where Amundsen had erected the Norwegian flag about a month earlier (picture taken from the walls in the South Pole Station). Right: The theodolite Shackleton used on the expedition which brought him in January 1909 as close as 97 miles from the South Pole (picture taken in the Canterbury Museum in Christchurch).

Just to see how accurate one can do these measurements with very simple means, I measured the length of the shadow of a flag pole in the IceCube construction area (see picture). For the given height of the pole of 2.13 m, I measured about a 5.50 m shadow length. From this, I calculated that the angle of the sun over the whole day was about 21 degrees. That means we are still more than two degrees away from the maximal angle of 23.4 degrees corresponding to the dip angle of the Earth’s rotation axis.


Left: The flagpole with which I confirmed that the shadow length did not change during the whole day. Right: The sun halo of 22-degree radius which extends below the horizon.

About a week before, one could see a spectacular sun halo which makes a 22-degree circle around the sun. In the picture, you can see that the halo reaches under the horizon, meaning that the height of the sun was less than 22 degrees. From a rough evaluation of the picture, I obtained about a 20.4-degree height of the sun, which is about right for November 23 when the picture was taken.

I will now measure the shadow of my selected flagpole every day (and when I leave, ask a colleague to do it) to confirm that the shadow becomes shortest at the solstice at December 21. You can easily study the course of the sun in your region by observing the shadow of a pole over a day and over a longer period. You could then, for example, confirm that when the shadow of my flagpole is shortest, yours, if you live in the northern hemisphere, should be longest. You might have a problem that the sun does not always shine -- at the South Pole the sun shines nearly always in the Antarctic summer.