Lines of Position

I was in my early twenties when I first learned about celestial navigation. I had always had an interest in astronomy, ever since I was a kid. I was a fairly knowledgable amateur astronomer as a teenager, and I majored in astronomy in college, so when I joined the Navy I managed to finagle myself into the Navigation Department of a missile destroyer. I’d never been exposed to navigation before, but I soon fell in love with it–it fit right in with my interests and background. My shipboard training was in the practical aspects of piloting and dead reckoning, plotting and chartwork, publications, electronics, and aids to navigation. I was introduced to celestial, and even worked out a position or two as part of my training, although in the modern Navy the sextant is rarely used, and then only by the officers and senior enlisted men.

Still, I loved the work, and after going back to school and finishing my degree, I became an avid sailor and had a chance to sharpen my wayfaring skills further. But it wasn’t until many years later, a married man with a responsible career, that I decided I would buy a proper yacht: one
capable of crossing an ocean. I realized I would need more than simple piloting and dead reckoning skills, I needed to master celestial navigation. I bought a professional sextant, picked up a couple of books on the subject and taught myself the arcane art of determining my position at sea by sighting distant objects in the solar system and the galaxy.

Celestial is really not that difficult, especially for someone with my background. It all looks very mysterious and remote, but basically it has been refined to a long and involved procedure of looking up numbers in published tables and adding and subtracting columns of figures. Knowing the mathematics, (mostly high school trig), is not really necessary. It has been reduced to a series of numerical recipes that can be memorized. With my understanding of the math and science, it was a bit more interesting for me than for others, but it is important to keep in mind that we’re not talking brain surgery or particle physics here. Celestial navigation is just accounting, a lot of rules to learn and some adding and subtracting on preprinted forms that keep you from losing your place and to remind you what comes next. It’s all been designed by geniuses to be done by idiots. I would compare it in complexity to figuring out the taxes for a small business, except navigation doesn’t change the rules on you every year. The physical skill of using the sextant to make celestial observations is comparable to firing a rifle. Anybody can do it, and after a few dozen shots you will get good enough at it to not embarrass yourself. Sharpshooter skill is not really necessary.

But although the practice of celestial navigation can be reduced to a mechanical sequence of steps, it helps to learn it if you actually understand what it is you are doing. Learning celestial can be much more than simply generating an “X” on a chart, it ties together every aspect of navigation; piloting and dead reckoning, as well as mathematics, astronomy, timekeeping, the calendar, cartography, and geography. If you can put it all together, it makes sense in such a way that you no longer need to memorize the steps, it becomes an integrated body of knowledge, you grasp how it all fits, and it gives you an immense confidence and peace of mind that is of great value. You can still get lost, but being lost will never terrify you again. You and your ship become part of the sea, connected to the world, the heavens themselves. There is no feeling quite like it, and once you understand how to do it, it fills you with immense pride that is difficult to communicate, but that others can sense in you. And if you’re the only one who can navigate, your crew is not likely to mutiny, either, at least not when you’re out of sight of land.

Every star and heavenly body is located in the sky, and there is a spot somewhere on earth where that star or body is directly overhead at any given moment in time. (The earth spins around once a day, and flies around the sun once a year, but if you know the time and date you can correct for that.) The Nautical Almanac tells you where in the sky that body is at any time. The sextant measures how far away that object is from the horizon, which allows you to calculate how far it is from that point directly overhead, so that allows you determine how far away you are from that spot directly underneath the body. If the star is 40 degrees away from your horizon (50 degrees away from your zenith), then you are 50 degrees away from its known geographical position, and a degree is 60 nautical miles. That’s all there is to it.

In practice its a bit more complex. First, you make a rough guess of your assumed position. It need not be accurate, anywhere within a hundred miles or so is good enough. Then you determine the elevation of the body above the horizon with your sextant, noting the exact time of the observation. You then go through a rather involved table look-up procedure to determine where the star is (from the almanac) and another one to determine where it should appear in the sky at that moment. Comparing the distance you measure from the one you expect tells you how far away you are from your assumed position; you draw a line on the chart, and you are somewhere on that line. After repeating this process for several stars, your result is several lines on the chart. Where they intersect is your position. How closely they intersect gives you a rough idea of the error of your position (which may vary considerably due to conditions, your skill as an observer, and mistakes such as misidentifying a star or mathematical blunder). Under ideal circumstances, you can locate yourself to within about a half-mile. In general, your true position will be within several miles of the position you calculate.

Once you’re practiced, the whole operation takes about an hour, most of it spent with your books and tables, scribbling furiously. You go out and identify and observe a half-dozen or so stars with your sextant, noting the readings and the exact time of each observation. Two observations is all you really need, but several more will allow you to discard any obvious errors. You then do the calculations for each star, drawing the lines of position for each on the chart. Where the lines cross, corrected for the motion of the ship during the interval, is where you are. In general, you do this twice a day at sea; at twilight, when it’s dark enough to see the navigational stars but still bright enough to see the horizon. At noontime, you can can get a simple latitude by shooting the sun. Identifying stars is easy, you can use a gadget called a star finder until you learn how to use the star chart printed in the almanac. After a while you will learn their names and they will become old friends.

The question I’m most frequently asked is “What do you see when you look through the sextant?” The instrument is basically an arrangement of mirrors that allows you to look in two separate directions at the same time, superimposing both images in the field of a small telescope. A reading involves twisting a knob until the glowing dot of a star or planet, or the edge of the sun or moon, just touches the horizon. At that moment you note the time to the second, and read the angle marked on the instrument.

By the time I had taught myself how to do it, I was laid off from my posh Silicon Valley job and had to shelve my plans to go sailing indefinitely. Over the next year, as I looked for work and went through the money I had saved to buy my boat, celestial navigation became a part of my life. It kept me going through a stressful time, a time when I came to question my own ability to earn a living and support my family. But no matter what, I could take some comfort from knowing I could take a ship anywhere on the planet the old fashioned way, by using the stars and a compass.
I took several offshore trips with my sailing friends so I was able to satisfy myself that I had the practical skills as well as the theoretical knowledge. I also took the time to develop navigational software that ran on a pocket calculator, a means of digging deep into the intricacies of the spherical trigonometry and nautical astronomy involved. By the time it was over, I considered myself an expert.

I had hoped to sell my software, and perhaps earn a living as a yacht navigator on offshore races or as an instructor, but the times had changed–while I was learning the craft, inexpensive Global Positioning Systems became ubiquitous on all but the smallest boats, celestial became as obsolete as Morse code telegraphy, hard-hat deep sea diving, or muzzle-loading firearms.

No one seriously studies celestial any more, except as a hobby. The essential skill that carried the world’s commerce has now become a pastime for dilettantes, a quaint art for armchair sailors. Real mariners are better off spending their time learning first aid, or diesel repair, or any of a hundred other essential shipboard skills than they are in investing the time and effort to learn celestial, and the constant practice required to keep the skill current. Short of total war or a breakdown in civilization, it is highly unlikely the satellites will be allowed to deteriorate while the Nautical Almanac is still faithfully published for the convenience of navigators.

But I still have my sextant, neatly packed away in its polished hardwood felt-lined box. It is a beautiful instrument, with an indescribable feel and even a smell to it, from the lubricants and the mahogany. I take it out occasionally and simply admire it, and once a year or so I take it to the beach, shoot some sights and calculate a fix, just to prove to myself that if I had to, I could still guide my ship wherever she needed to go. It’s a good feeling, but a sad one. The sextant has become a memory of my youth, relevant only to me, and a reminder that times change irrevocably. It can take me anywhere in the world, but it can’t take me back. Its ties to the past are there, of generations of seamen braced against a bulkhead on a rolling deck, bringing a star down to earth. I am tied to that past, but it is a past, I am in the last generation to have used a sextant as anything other than just an amusement. There is some grandeur to that, but also a great sadness.