Customer Reviews

Celestial Navigation in a Nutshell (Seafarer Books)

5 star:		(6)
4 star:		(4)
3 star:		(0)
2 star:		(1)
1 star:		(2)

 

 

I found Celestial Navigation in a Nutshell easy to follow and the diagrams made a distinct contribution to my understanding. I also liked Schlereth's informal, personal style. It too made this scary subject more readily available to my teensy mathematical mind.

I found his use of the plotting sheet a unique and helpful addition. I never came across this gimmick before. I was also grateful for the large easy-to-read type.

I'm a student pilot (hopefully for not much longer!) and navigation is very interesting to me, not to talk of very important as well. I've heard of celestial navigation as being the ultimate form of navigation and I was interested in finding out more about it by reading various books but each time I did, I had to give up because I did not have the necessary PhD in astrophysics to understand what the author was trying to say.

So, it was with a little trepidation that I approached reading this book by Schlereth and to my pleasant surprise, celestial navigation makes sense! His use of simplified theory may not be to some people's taste but at the end of the day, I'm not studying for an exam, I'm trying to understand what celestial navigation is and how to use it. This book teaches you how exactly to use it and that's all that matters to any good author and should to any good reader. I can now go outdoors with a sextant and the necessary tables and find out where on earth I am, correct theory or no!

Hewitt Schlereth wrote this book to explain the use of the HO249 tables to fix one's position on the earth using the known positions of the sun, moon, planets, and distant stars. I would also recommend reading this book if you intend to use another method of sight reduction, such as George G. Bennett's "The Complete On-Board Celestial Navigator" (ISBN: 0071396578). Schlereth gives a good introduction to the celestial bodies used for navigation and how to use them.

Schlereth's examples show the relevant tables, highlighting the values used. He makes it clear how to enter the tables correctly every time, and gives a few tips on how to avoid transcription errors when "taking out" the numbers you need.

He begins the book with a little trigonometric fiction -- that we are interested in the angles between the sun, the "position" of the sun on the surface of the earth, and the observer. Of course, this is a bit of nonsense, as another reviewer, Nathaniel Meyers, has pointed out. Schlereth corrects himself in a later chapter, and I think he could have better begun with the story of how the famous Greek philosopher calculated the circumference of the earth thousands of years ago.

The eager student should work through the examples thouroughly. Be on the lookout for the error in transcribing one of the sights in the example of the approach to San Salvador -- the first fully-plotted example.

This book is a good introduction to celestial navigation -- a useful place to start before going on to more advanced sources of information.

In Chapter 3 page 9, as far as I've gotten, for example he explains that if you take the angle measure of the sun (or any object) and subtract from 90 degrees you get the angle measurement of your distance from the point of the earth directly under the sun (the GP). This is very true and is the fundimental of celestial navigation. But his explanation why is patent nonsense and absolutely wrong. He says one can make a triangle between the sun, the GP of the sun, and the observer. This is wrong. The sun is of such a great distance from the earth that for the intents and purposes of celestial navigation the sun is infinitely far away and all rays (and views of the sun) are parrellel to each other. So rather than a triangle, you'd get two parellel lines connected by a curved arc (the surface of the earth) with the line at the GP going straight up (perpendicular) to the curve and the line at the observe going up at the measured angle but parellel to the other line. Then he says, referring to his triangle that as all triangle angle add up to 180 degrees and the GP angle is 90 degrees (it goes straight up) so the Apex (angle at the sun) is 90 - measured angle. Angles of a triangle add up to 180 only if the sides are straight lines. If the sides are allowed to curve the angles can be anything. In fact if (as his triangle does) two sides are straight and the third curves away the sum of the angles are always less than 180. Then he concludes that the angle of the sun is equal to the angle curve of the earth because that is the side opposite it. He calls this "knowledge of a little trig". I call it out right nonsense without knowing the height of the triangle (in this case the height of the sun) you can't conlude any relationship between the two. In fact if you did draw a big enough triangle to reach the sun the angle at the sun would be miniscule, extremely close to zero, and nothing at all close to 90 - measure of the sun on the surface.
The correct explanation would be to draw the two parrellel lines, Draw the angle at the center of the earth, draw a perpendicular (straight across) line crossing the two parrellel lines. THe result is a quadrangle. Quadrangle angles add to 360. The two angles by the crossing line are 90 each and don't mean anything but are just used to demonstrate that the remaining to angles, the center of the earth (which is equal to the angle measurement of your distance to the GP) and the angle from the center of the earth to you to the sun add up to 180 degrees. Since the angle from the center of the earth to you to the sun is the sum of the angle from the center of the earth to the horizon (90) and the angle from the horizon to the sun (the measured angle, then the measured angle and the angle measurement of your distance to the GP add up to 90. That's not a "little trig" but "a lot of forgotten geometry and hand waving" but at least it is true rather than utterly false.

So, if I can't trust the writer in the theory, I can't recomend the book even if all of his celestial navigation is correct.

I consider myself relatively well educated, but I simply could not make good use of this book. The author's extensive use of acronyms and poor grammar made it very difficult to 'follow the plot' so to speak. I continually had to thumb back and forth to find the definition of terms. I understand that many scientific topics are full of jargon, but a book should help the reader ease into the use of terms, not simply throw them at the reader and hope for the best. I suppose one way to teach a kid to swim is to toss them in the pool and let the work their way to the side, but one assumes an instructor claiming years of experience would have a more effective method.

I assume each chapter was meant as a discussion of a particular topic, but the topics don't always follow one another, and many times it's left to the reader to figure out just what the chapter was about--after it was read--and how that chapter relates to previous material. Frankly this not only reflects poorly on the author, but on the publisher as well. Who proofed this? Is this the kind of book they consider good enough?

I also understand that people avoid math, and there's an impulse to simplify numerical problems as much as possible. However, the author avoided math so much that there is none. It takes more arithmetic to balance a checkbook than is demonstrated in this book. Navigation is a topic born in equations. In my opinion one can't understand the methods if one is incapable of performing the mathematical steps involved. And it's just not that hard.

If you're looking for a simple book that introduces a few basic portions of the topic, this might be it, especially if your attention span is limited to a few pages at a time. If you're looking for a book from which to learn, pass on this one.

With modern GPS navigation now omnipresent, why would anyone want to use celestial navigation? Because it's fun, it teaches some valuable lessons about how celestial bodies can show where you are on the earth's surface, and it could be a useful backup in case of loss of GPS due to dead batteries or loss of satellites. This book teaches the subject in easy to understand language, and with just the right amount of humor. All you need is a sextant (which can be obtained, used, for less than $100) and a nuatical almanac. Since this book was published some free computer programs have become available that will let you enter the time and the sextant reading and produce an LOP (line of position) eliminating the need for the almanac. You can practice taking sun shots at home on land, even if you can't see the horizon. In a few hours you can become pretty good at it.

I know this book is kind of simple for advanced Celestial Navigation but that's why I love it and recommend it. It breaks it down in a way that is simply understood. If you are going for an unlimited license you will need to go further in-depth but I recommend you start here. I am a 2nd mate unlimited (hawsepiper ) and I am always recommend this book to prospective AB's that are looking to advance. You will need more but this is a great book to read if you are interested in this subject.

This book gives a great overview of celestial navigation in a manner that is fairly clear to someone with a solid math background. If you were at all iffy on Trig or more advanced geometry, this book probably isn't for you, but also, if that's the case, it's better to stick with GPS (where someone else has already done the math) anyway. I'd still want an experienced navigator alongside if I sailed beyond sight of the shoreline, but this book gave me a reasonably complete and rigorous explanation of how celestial navigation works, which is what I was looking for. It's a good intro course for sailors, a solid summary for the rest of us.

Celestial Navigation is a "must" for aspiring new navigators and old traditional sailors like myself. This book knocked all the rust off my old-fashioned navigational skills.

The book was a gift for a new Eagle Scout. He was quite pleased.