Sailing by Starlight: the lost art of celestial navigation

Posted: 10/01/2010 in all marine news

By Southern Fried Scientist

Today it seems rather trivial. We have a host of technologies available that allow us to precisely pinpoint our location in the world. Even without the smart phones and GPS network, we still have reliable road maps, decent signage, and large easily recognizable landmarks.

But what if we didn’t? Pretend for a moment that you’ve been blindfolded, spun around, and dropped somewhere in the world. You have no reference point, no maps, no landmarks, and, to make things just a bit more difficult, you’re floating on an ocean that’s constantly moving, so you can’t even maintain a stable position.

This is the challenge mariners faced since we first left sight of shore.

So now I’ll ask you again, where are you? It’s ok if you don’t know, we’re going to figure it out together.

First, I have to assume you’re on Earth. If you’re not on Earth, you’ve got bigger problems to deal with. The next step is figuring out which hemisphere you’re in – the Northern or Southern. This may seem trivial, but with no GPS, maps, or even landmarks, how do you know which side of the world you’re on? Obviously, since this is a post about celestial navigation, you have to look up.

If you’re lucky enough to be in the Northern Hemisphere, you’ll probably recognize Ursa Major and Ursa Minor (the big and little dipper or the two bears). If you’re in the Southern Hemisphere, you’ll probably recognize Crux (the Southern Cross) and maybe Centaurus. I say it’s lucky to be in the Northern Hemisphere because what you’re actually looking for is not a star, but a fixed point in the sky. The planet is spinning, and because the planet spins, the stars in the sky appear to rotate in a circle. If you’re moving, and the stars are moving, you can’t use them as a guide, either you or the stars must be stable.

There are two points in the sky that don’t move, the Celestial Poles. These are the points in the sky that fall along the line of the earth’s axis of rotation. In the Northern Hemisphere, there is a star, Polaris, that falls almost exactly at that point. In the Southern Hemisphere, there is nothing to mark the southern celestial pole.


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