Wouldn't it be great to have a time machine?
Just imagine all the cool things we could do. We could travel back into time to straighten out everything we goofed up in our past, or speed forward to preview the future. We could even see the same starry heavens pondered by such luminaries as Aristotle, Copernicus and Galileo.
Well, for the first two I'm afraid you're on your own. As for the last one, I think I can help. In fact, if you'd like to see the very same sky viewed by anyone in recorded history, all you've got to do is go outside and look up.
For the most part, the stars haven't changed much in all that time. Orion is still Orion; the Dippers are still the Dippers. There are subtle changes, of course. The planets and the moon continually shift their positions among the fixed stars. And there's one other change that occurs in the sky – one that most of us have never noticed. It's what astronomers call precession.
Precession is a wobbling of the Earth's axis – the same kind of wobbling experienced by a spinning top. But, while a top's precession is easy to watch, the Earth's requires some 25,800 years to complete just one cycle.
Because of this, the positions of celestial objects tend to shift slightly over time. Precession causes the Earth's axis to point outward in slightly different directions over the millenniums. Right now, our north axis points toward the star Polaris, making it the North Star. But long ago this wasn't the case. In fact, back when the ancient Egyptians were building pyramids, our north axis pointed more toward the star Thuban, located in the long, sinuous constellation of Draco.
You can find Draco winding its way between the Big Dipper and Little Dipper in the northern sky after dark. The four stars at its lower end form the dragon's head but are known to amateur astronomers as the “lozenge.” And toward the tail end of the Dragon lies the faint star known as Thuban – Arabic for dragon.
If you wait another 20 millenniums or so, you'll again see Polaris and the Little Dipper move away from the north celestial pole, and watch as Thuban and Draco take their place – a sort of back to the celestial future.
© Copley News Service
