How do Santa's reindeer find their way?
Stephen McCarronBelieve it or not, the navigation of Santa's reindeer, and thus much of Christmas, owes everything to geology.
How did Santa's reindeer find their way back home from anywhere in the world, long before the days of satellites and GPS?
They must have used the same trick that all sailors have used to sail the world's oceans, to tell north from south, by day and night. The trick is to use the natural magnetism of the Earth.
For centuries, sailors have used magnetised iron needles to create compasses that always point northwards, exactly what Santa's reindeer would need to know too!
What else would they need to know to get back north to the Arctic from Ireland or anywhere else? But how does a magnetic compass or a reindeer's magnetic sense work?
Both use the force field coiled around the Earth that runs in invisible lines out of the ground near the North Pole, arcing high up into the air and down all the way to the South Pole.
The force field lines are thought to be coming from deep within the Earth itself, by processes never seen but long mapped and studied by sailors and geologists on the Earth's surface.
The field is thought to be generated by the slow movement of iron-rich molten rocks making up the Earth's outer core, thousands of kilometres down into the Earth.
A magnetic mineral, known as magnetite, is found within iron-rich rocks such as basalt that have come up out of the Earth in volcanoes.
Magnetic basalts show that magnetism can be found and stored in rocks, and it is thought this or similar iron-rich minerals create the Earth's magnetic field due to vast currents moving within the very hot, highly pressurised outer core of the Earth.
Over long, geological time spans it has been observed in geology that the field also moves, and can flip completely from north to south!
But today, and for all the centuries known to man, high above the Earth the magnetic field is present, guiding and also shielding the Earth from harmful solar radiation.
Without it, life may have never survived on the Earth's surface.
Across the ever dark Arctic winter skies the field produces the Northern Lights or Aurora Borealis as it soaks up this radiation.
The Aurora's wispy glowing streamers show up the ghostly force field lines, celebrating the safe return of the reindeer home.
QStephen McCarron is a lecturer in the Department of Geography NUI Maynooth. His research interests involve the search for geological evidence of former ice sheet extents and dynamics on the island of Ireland and on its continental shelf