How to spy for 'Santa's sleigh' in the predawn sky

Look to the southwestern sky at 6:13 a.m., for what looks like a fast-moving star growing brighter as the station exits Earth’s shadow. It will travel across the sky, setting on the northeast horizon five minutes later. With lows in the upper 20s expected, bundle up and have some hot cocoa.

All eyes on the North Pole Christmas Eve, but which one? There are actually two North Poles, geomagnetic and geographic.

The geographic North Pole is located 90 degrees north latitude and, by convention, zero degrees west longitude and has no time zone. It is reasonably stable, moving only a few centimeters per year due to changes in the distribution of the Earth’s mass, most recently due to melting polar ice.

There is no land at the North Pole, only declining amounts of ice with about 14,000 feet of Arctic Ocean beneath, The nearest inhabited place is more than 500 miles away at Alert in Canada’s Nunavut territory. Most of its fewer than 100 residents work for Environment and Climate Change Canada (Canada’s version of the National Oceanic and Atmospheric Administration) or are gathering signals intelligence for the Royal Canadian Air Force.

It is possible to visit the North Pole, especially in the spring and summer when navigable gaps appear in the ice. The U.S Navy’s fast-attack submarine USS Hampton (SSN 767) joined the Royal Navy submarine HMS Tireless and surfaced at the North Pole April 19, 2004, in a joint mission. The crews met on the ice for a soccer game while scientists aboard collected data and performed experiments.

Sunset wouldn't disrupt that April game for another 157 days. Movies that depict Santa leaving his workshop on Christmas Eve in the dark of night have it right. The sun sets a few days after the September equinox and doesn’t rise again until a few days before the March equinox.

The geomagnetic North Pole is far less stationary, moving northward an average of 25 miles per year. This occurs because Earth is like a giant electromagnet. The inner and outer cores spin at different rates, creating a dynamo effect. Changes in that effect cause the geomagnetic North Pole to change as well.

Changes in magnetic north can cause expensive changes at airports. Once the difference between true and magnetic north shifts more than 10 degrees, runways must be renumbered, making it necessary to repaint those huge numbers at the end of runways and update dozens to hundreds of signs along the runway.

This is necessary because runways are numbered according to their magnetic compass bearing rounded to the nearest 10 degrees, with the last digit dropped. When that magnetic bearing changed enough, Tampa International Airport was forced to shut down for several days in 2011 to update three runways. Similar changes have been necessary at airports in Palm Beach, Miami and Fort Lauderdale, Fla.

No similar changes are expected at Raleigh-Durham International Airport in the near future. RDU’s runway 5L-23R was built in 1986 on a bearing of 45 degrees to true north. According to the Federal Aviation Administration and NOAA, the World Magnetic Model (WMM) mapping magnetic variations across the globe last listed RDU’s variation from magnetic to true north at -9.1 degrees, with a continued westward migration of .04-degree forecasted each year. The next model is expected in 2020.