Astro Navigation & Sextant

[Skylark]

Sorry but no. The easiest way to identify stars is to hold up your ipad with Star Walk in front of your face.

All well and good but not a great deal of help mid Atlantic.

Star sights are relatively "advanced" along the astro navigation skill level. Most people can find The Plough, hence Polaris and this is good for latitude. The closest I'm likely to get to Betelgeux is to watch Hitch-hikers Guide to the Galaxy!

Once you have mastered sight taking and reduction using the sun, the easiest way, IMHO, to progress to civil twilight start position fixing is to use AP3270 Vol 1. A bit of work in advance will give you Zn and Hc for the 7 selected stars. Work east to west, in northern hemisphere, set altitude on the sextant and your nose to Zn and, hopefully by magic, there will be a star in your view. You don't need to know its name and you don't need to try to identify it beforehand. AP3270 Vol 1 will also tell you the three best for a fix and also their magnitude (brightness). Only the clouds should put a stop to your fun.

I did the YM Ocean one-to-one with a master mariner, retired sea capatin. He showed me his Hydrographic Office Star Identifier. I found one on e-bay and duly bought it. I'm happy to be shot down by those with more experience but it's not the easiest thing in the world to use. My vote for star work remains with AP3270 Vol 1.

As always on this subject, a great thread with a lot of helpful information. More, please!

 

[Ex-SolentBoy]

All well and good but not a great deal of help mid Atlantic.

!

What makes you think it wont work mid-atlantic? My ipad has a proper GPS chip in it. It can find your position whether you are connected to wifi, 3g or not.

To prove this, take a 3g ipad outside. Turn off your wifi, take out your 3g chip and turn it on. It position finds (and star-finds) within seconds.

 

[timbartlett]

I may be dreaming but I think that I recall that the RYA has recently published a course workbook. May be worth adding to your library.

You're not dreaming.Published last year. But it's a bit more than a course workbook: it's intended as a complete introduction to astro, from first principles (if the sun is low in the sky, then you must be a long way from the place at which it is directly overhead) through using and looking after a sextant, to star and planet sights, Polaris, and a brief mention of the moon (all based on Air Sight Reduction tables).

 

[jdc]

identifying stars

I've nothing against using a computer to learn the stars but you don't need a GPS, a very approximate DR position which you enter manually will do fine. I like 'Stallarium' which runs on a laptop.

Before the days of computers, or GPS for that matter, and before getting the excellent pre-computed air tables, I found that it was really hard to get star sights in the evening. This is because one needs a horizon, which means that it can't be really dark, which means that only the brightest stars are visible, and the constellations invisible. Hence I could never identify the stars unil it was too dark to use them.

The solutions were (1) to take star sights at dawn: you've ages to identify the stars while it's still pitchy, and then can 'hang on' to the brightest ones until the horizon is visible; and (2) having at last figured out which were the bright stars you could see in the evening, remember them for the next evening (this took me nearly 24 hours to figure out;-)

 

[bluemerlin]

best astro-nav book

Try Astro-navigation from Square One - by Alan Murray pub 2010 - superb.................

 

[Jamesuk]

Can anyone recommend any good books for a beginner to learn astro Navigation and using a sextant.

TIA

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The RYA Astro Navigation skip out the first 4 pages the rest is excellent, Blewitt is really good but I found the Astro Nav book from the RYA easier to learn from. Although the best teacher can be found at your local Maritime Volunteers Service Station where the old dogs there used to do it day in day out for there XX years at sea.

 

[bluemerlin]

Astronav book

You could try Astro-navigation from Square One - 2010 edition v useful - covers all the difficult theory with good examples and cracking diagrams - is also available as e-book.

 

[Talulah]

You're not dreaming.Published last year. But it's a bit more than a course workbook: it's intended as a complete introduction to astro, from first principles (if the sun is low in the sky, then you must be a long way from the place at which it is directly overhead) through using and looking after a sextant, to star and planet sights, Polaris, and a brief mention of the moon (all based on Air Sight Reduction tables).

I use the RYA Astro Book by Tim Bartlett when teaching Celestial Navigation.
I have used some of the other books mentioned but Tims is easy to follow, well laid out, clear, concise and cheap enough to give away to students.
I have found with a lot of the other text books that at one point or another they make a leap from 'a' to 'c' and the student is missing the knowledge of 'b' and gets stuck.
I just wish there was an errata with it to fix the errors.

 

[KellysEye]

>noted that he does not use the "Air Tables", which most yacht navigators use;

I'm not aware of any yachtie using Air Tables. V bomber pilots and early commercial flights obviously used them plus people like Francis Chichester in his flying days.

To answer the question we found Mary Blewitt's book the best. We looked at the others and found them overly complicated.

 

[capnsensible]

>noted that he does not use the "Air Tables", which most yacht navigators use;

I'm not aware of any yachtie using Air Tables. V bomber pilots and early commercial flights obviously used them plus people like Francis Chichester in his flying days.

To answer the question we found Mary Blewitt's book the best. We looked at the others and found them overly complicated.

EEK! Mary B uses Air Navigation tables!! AP 3270 in three volumes.

So does Tom Cunliffe (the best in my opinion) and of course, the RYA course.

 

[Talbot]

>noted that he does not use the "Air Tables", which most yacht navigators use; I'm not aware of any yachtie using Air Tables. V bomber pilots and early commercial flights obviously used them plus people like Francis Chichester in his flying days..

I use the air reduction tables. They were even taught on the RYA Ocean Yachtmaster course.

Saves a lot of figuring out.

 

[bbg]

This is an impressive thread. The OP would have had time to learn everything there is to know about celestial nav, and sail across the Atlantic and back half a dozen times, in the time this thread has been running!

 

[bluemerlin]

Air table/marine nav tables and an Asto free e-book

Its all a matter of the accuracy you require. If the navigating officer on one the ships of Her Majesty's ever diminishing navy, one might be required to adjust a sight for air temperature and pressure and get the accuracy of an intercept on a position line to well below 0.2 of a nm. In our real world, the Air Nav tables, incidently published for mariners as NP 303 Rapid Sight Reduction Tables for Navigation vols 1-3, will or should give you a position within 0.5nm or so. NP 401, Sight Reduction Tables for Marine Navigation give, or are said to give, an accuracy to about 0.2.

Of course and realistically, we would be more than happy to get an accuracy to a mile or a little more.

I agree that Tim Bartlet's RYA book is good but it is a bare minimum in my humble opinion.
The current RYA Yachtmaster Ocean course is also, because of the necessity of time, a relatively superficial look at Astronav.
I also agree that many texts take leaps between a and z on occasions. I'm quite happy to forward to anyone an ebook copy of Astro-nav from Square One to Ocean-master 2011. (mainly as I am the holder of the copyright and the book comes out in a couple of weeks!). I would be most interested to hear anyone's views on it as I have very intentionally written it so as to cover every aspect of Astro - NOT intending to make any money from it, merely to explain the usually unexplained and to foster support for this dying art.
If you want a free copy - email astronavsq1@gmail.com