I had a small dinner party last night so that some friends could come over for some ‘za and beer and catch up on the latest antics of Nancy Botwin and company on Weeds. Per the old saying, “A good time was had by all.” Or to put it less passively, “As usual, we had a blast! (And that Nancy… craaaaaaa-zy!!)”
However, in the course of conversation I realized not everyone knows about the magic behind our north star (Polaris by name) and found myself taking the virtual podium to explain. It’s one of those things that’s common knowledge to many, but may come as a complete surprise to others.
So for those of you not familiar with the navigational magic behind the north star, here’s the deal.
I expect that just about everyone knows that there is a north star. Anyone living (or visiting) the northern hemisphere—the lands and seas north of the equator—has probably even seen the north star. And it should be common knowledge that when you’re in the northern hemisphere, the north star is always damn near exactly dead north. (In fact, it’s a better indicator of north than a compass, because magnetic north is significantly different than true north.)
But did you know it also tells you how far north you are of the equator? It doesn’t just give you a bearing on which way is north, it also gives you your exact latitude.
And it does so in a very simple manner: the angle of the north star above the horizon is your latitude.
It’s that simple. If you’re standing on the north pole, the north star is straight up, 90 degrees overhead (considering the horizon as zero). On the other hand, if you’re standing on the equator, the north star is on the (northern) horizon, which is zero degrees.
Anywhere between the north pole and the equator, the north star is the same number of degrees above the horizon as your latitude. For example, if you’re standing at 45 degrees north latitude, the north star is 45 degrees above the horizon.
The happens because the north star is very far away (over 400 light years), and this means its rays all arrive at earth in basically a flat line. No matter where you are on our tiny earth, when you sight on the north star you are looking in the same direction as anyone else sighting on the star. (This is true for all stars, including the sun.)
If the star (or the sun) is the point of a triangle, and two observers on earth are the two points at the base of that triangle. The difference between the base points—which can never be larger than the diameter of the earth, is incredibly tiny compared to the legs of the triangle.
Remember your high school geometry; the angles of a triangle always add up to 180. If the legs are astronomically huge, and the base is just earth-sized, then the angle of the tip is very, very close to zero, which means the angles of the two base points (which are equal) split between them the whole 180. Bottom line: the triangle legs meet the base at 90 degrees minus an insignificant amount.
There are a couple of things about the North Star that are pretty incredible. The mere fact that there is a north star is a coincidence. It just so happens that Polaris is at the right point in the sky. And it hasn’t always been there. Over a period of about twenty-five thousand years, the earth’s north pole moves about the sky in a circle (the axis precesses). It just so happens to point at Polaris during this age of humans on earth.
And it isn’t just that there happens to be a star in the right spot. Polaris is bright enough to been seen even in the blast of city light; most people in the northern hemisphere should be able to see it from their backyard. And not only is Polaris bright enough, but it has the Big Dipper and Little Dipper that help you find it.
So you can ask yourself: Does this happy set of circumstances in the sky provide an edge for northern hemisphere explorers? Or is it a bit of a celestial gift that gave humans a helpful edge at just the right time in their development?
Science will, of course, insist on the former answer, and it is the most logical choice. What makes it all so intriguing is how many interesting coincidences have occurred to bring humans to where they are. We are the end result of an astonishing number things going exactly right. If nothing else, it should be a source of great wonder, even if it doesn’t make you wonder, at least from time to time.