| FAQs |  |
Celestial Nav |
No. Not for the course itself. You will, of course, need a sextant once you complete the course and are ready to go out and do your sights, but to learn the subject with our materials you do not. There is an extensive section in the notes on the use and care of a sextant and good practice exercises on reading the dials using graphics. After that, in the notes the problems start out saying the sextant read such and such at this particular time, and with that info you carry on with the problem from there. We do have very good prices on sextants, however, if you do choose to purchase one later on. Index
... "Sight reduction" is the book and paperwork that takes you from sextant sights to a position on the chart. This is done with two books, the Nautical Almanac and some set of sight reduction tables. There are several options on this latter, and that is what the question is about. Our course covers essentially all sight reduction methods. The notes themselves include sample pages from Pub. 249, which is in a sense the main ones we use. Our work forms, however, are designed for use with Pub 249 and Pub 229, and the instructions in the work forms go over the use of Pub 229 and Pub 249. We provide sample pages from Pub 249 rather than 229 simply because we can generate more practice problems with fewer sight reduction table pages using that set. We also provide special work forms for doing sight reduction with the NAO Sight Reduction Tables (those from the Nautical Almanac Office that come free of charge with every purchase of an Almanac). Our forms are exceptionally convenient and indeed make this set of tables a viable option. We also cover sight reduction by calculator. Index
... We strongly recommend the traditional half-silvered mirror over the optional one called by various names such as "full-view" or "whole-horizon." Here is the story: If you have never taken a sight before and are presented with a sun in midday with a dark blue sea and light blue sky, and you were asked to compare the two types of sextants, you might indeed choose the full-view style. It will at this first use of a sextant in these ideal conditions seem easier. And indeed it is this reaction that has led many new users into choosing this option. What you will soon learn, however, is that this is indeed a very easy sight, and regardless of what sextant you have in your hand, you will in a few minutes of practice be doing it just fine with a traditional mirror. With this standard type of sextant (used since 1750's) you do have to coordinate keeping the sextant pointed at the object as you move around some and rotate (rock) the instrument. With the full-view model, you have broader leeway here and this is easier. On the other hand, for other sights, things are completely different. The full-view mirror works by splitting the light spectrum in half according to color, by means of special optical coatings on the glass — invented by Davis Instruments (or at least first applied to sextants by them), the folks who make plastic sextants, and later copied by other manufacturers. The surface reflects the bluish half and transmits the yellowish half. The net effect is you see at the same time light passing through it and light reflected from it — but only roughly half of the light intensity in each case. Hence the problem. For faint stars, you are losing half the light so the stars are more difficult to see. But that is not the main problem. The main problem comes in when viewing anything that is about the same color as the sky. A daytime moon in a "white" sky, for example, can sometimes not be taken at all with that style of mirror. Also when the sea and sky are nearly the same color — which is fairly often — then it is very difficult with this model to check the index correction. Another drawback shows up when you use the sextant for coastal piloting, either with vertical sextant angles or horizontal angles, such as the famous 3-body fix, which is such an accurate means of piloting it is usually called sextant surveying. You are looking at land overlaping land images where they differ only in the shade of color. These sights are rather signicantly more difficult with the full-view type of mirror. In a nutshell, "full-view" mirrors make the easy sights easier and the hard sights harder. We do not recommend them as an option for metal sextants. (As it turns out, the top of the line plastic sextant does come with them as standard equipment, but since these are more for practice or for backup than for primary navigation, it is not so much of an issue in that case and they likely serve a good purpose.) For completeness we should mention this exception. Very high sights (Hs >85°) are difficult because with the sun essentially overhead it is difficult to keep the sextant pointed toward the sun's direction — it's very figuratively like deciding which way is south at the North Pole. They are definitely doable, but it takes special techniques in both the sight taking and of course in the analysis. You cannot use conventional sight reduction methods for near-overhead sights. Well, for these rare sights, a full-view type of mirror makes them a bit easier than a split-view mirror. That said, we still do not change our recommendation. Index
... Yes, indeed you are. We have had more than 15,000 students in this celestial course over the years (that is not a typo....fifteen thousand) — that have taken this course successfully; many if not most have gone on to cross oceans or even circumnavigate. Men and women from every walk of life. From teenagers to couples in their 70's. We could not have carried on in this manner if we were not getting the subject across. We stand by every student. You have the invitation and encouragement to call us if questions arise that are not answered in the notes. We can make this invitation because after all these years our notes are thorough. All parts of the course materials start out right at the basics, and build up with clearly laid out, step by step examples. We have thought through not just the material itself over the years, but also how to present it. The pace of study is purposefully broken up, for example, between "book work" and plotting or hands on graphics work. All the answers are presented. We even have a special section in the front of the notes that addresses the issue of anxiety with learning this material. Over the years, we have had many people tell us that they have tried numerous approaches, but none had worked.... till now. This was the first course and teaching environment that had made the subject clear to them. And they went on to become good at it. Index
... Well, the real answer is you don't. You don't even need a boat to get to Hawaii or Bermuda, or take a trip around the world. You can do this by plane. It is faster, cheaper, and more comfortable. On the other hand, if you do choose a life at sea, then one of the fundamental rules of thumb that has been tested so many times we don't even have to go over it, is you must be prepared to take care of yourself. You must be self reliant. Murphy's Law was invented on a small boat at sea. Anything electrical is vulnerable after some time in the salt air, especially when it is being jarred, bumped, banged, and dropped (i.e. going to weather). Therefore we need some dependable means of navigation, and celestial is that. Needless to say, a hand-held GPS and spare batteries stuffed into a well protected vacuum sealed bag is a pretty good back up these days, but it is not at all bullet proof. Furthermore, you are still dependent on the availability of the signals. In any sort of worldwide military conflict, it is likely you would lose these, depending on where you were — you could lose the signals in a union dispute; it doesn't really matter... or as a result of a "pre-commissioning validation exercise!" See also question 724 of the new USCG license exam questions on GPS. But quite beyond all of that (the numerical likelihood of needing it), learning celestial is still a most rewarding venture. It will make you a better navigator even on inland and coastal waters — you must, for example learn how to do a running fix to do celestial and this could well pay off if you lost the GPS for some reason and were left with just one light shining through the fog; or you close in on a coast, but can then only identify one feature on the land (which is not a radar target), etc. Such problems are easily solved with a running fix. Once you learn celestial, it is also a trivial matter to check your compass with the bearing to some celestial body, even well away from any land marks and in a strong unknown current. You can't do this with GPS, nor any other instrumentation on board, no matter what it cost, and no matter if you are a ship or a sail boat. The only way to truly check your compass at sea is with celestial. And if the boom hits your compass or lightning strikes near by, or — much more likely — you simply realize that it never was checked before, then this is something you must do one day, etc.... And finally, there is a wonderful intellectual satisfaction that comes from leaning and practicing celestial navigation. It is a way to see science and math really come together and do something both tangible and useful. Learning celestial will also make you a better mariner because whether you show it or not, you will be anxious about your navigation if you are depending on something that you cannot hope to know anything about (i.e. GPS — it is a black box. You can just hope and pray that it works right... and you will only really know that on the last day). And when you are anxious, you are more likely to make a mistake.... and you risk the chance of exposing your anxiety to the crew which could undermine your leadership, which in turn could lead to all sorts of unpleasantness... In the long run, it's best to learn celestial, even if you are never going to use it. You will know you can if you need to, and that alone will make it worthwhile. If you plan to crew on other vessels, then knowing celestial will be an important part of your credentials and will certainly help you find a good position. And one last related thought: GPS is (in an abstract sense) just a version of SatNav (the Navy Transit System... now long gone) that happens to work efficiently. In short, we have had all-weather global satellite positioning for more than 20 years now. Yet there never was any consideration at all by the USCG to remove the requirement of learning celestial from an ocean license exam. And there is none now. To get a USCG license that is valid offshore you need to know celestial and pass a test on it. Whatever the reasoning behind that decision, it is many-fold increased for small boats at sea. Index
... You can indeed use a pan of oil or even a well-leveled plate glass mirror to take sights inland away from a true water horizon. If there is any breeze blowing, the surface must be covered with a piece of plate glass. Any ripples at all will disturb the process. Explorers used this method since early this century in the Arctic and in the desert (generally with small trays of mercury). For practicing the marine application of celestial navigation, however, this is not a very useful method. We do not recommend it for several reasons. First, it is not done like a normal sight. You look down at the pan, not straight out toward the horizon, and you align the objects for a sight in a different manner than done at sea. You must then sight reduce the data in a different manner than normally done. Also you are limited to only one half the range of the sky since the process doubles the altitude. In short, you are not getting practice with what you will actually be doing underway. You are just getting data that might be about right to practice sight reduction with. We can assure you, however, that celestial works, and doing the textbook practice exercises will do this job just as well as generating numbers this way. Furthermore, if you have any water at all around (a lake, or bay, or even river) that is a quarter of a mile or so across, then you can practice with the "dip short" method using the shoreline. This is a much more realistic way to practice. The method is described in detail in Chapter 2 of our course, or see discussion in Bowditch. This is not only a good way to practice, it is a technique that you might indeed need one day. Also if the distance (in nautical miles) across the body of water is equal or greater than the square root of your height of eye (in feet) above the surface, then you are looking at the true curvature of the horizon, not the actual shoreline, and do not even need to use the dip short correction. In summary, if you have any water at all around you, you are better off using it rather than a so called artificial horizon. Index
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As in the coastal course, the home study course materials are the same ones we use in our classroom course. The classroom celestial course is seven 3-hour classes plus a sextant practice class and a planetarium class. With outside work, we figure the classroom celestial course at some 50 hours of work. We assume the home study course goes a bit faster on average, and recommend you figure some 30 or 40 hours of work to go through all the materials. And as with the coastal course, there are extra materials included that you need not go through at first, and there are many practice problems which you may choose not to work at first. This will cause some variation within this time frame. To get the material we cover in the planetarium class, we recommend you read the Star Finder Book which is included with the course materials. For more information on these matters, we suggest you purchase our Emergency Navigation book. The latter includes extensive coverage of reading the sky: stars, sun, and moon. Index
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Yes, but this must be organized by the host location. Typically we do our regular courses at the regular fees, plus travel expenses, but we do them in a more compressed format, often over a long weekend. We have a minimum of 15 students, but typically if the organizers have a committed core of just 5 or 6, the rest can be found by local advertising. We leave it to the organizers to provide an adequate teaching space. We have done these in hospitals, high schools, law offices, and yacht clubs around the country. |
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