Which celestial navigation software?

[Frank Holden]

I've just spent a very pleasant hour skip reading through all 172 pages. That's a fine body of work, Frank. Do you mind if I keep a copy, are there any copyright issues?

I'm pleased that you like it.
No problems. No copyright issues. I wrote it for the Australian sailing magazine 'Cruising Helmsman in the early 1990's. About 5000 people signed up to do the 12 month correspondance course that went with it. The Mag had first publication rights so all mine to do with as I wish.

 

[Skylark]

Just want to add to this thread that Astro IS hard. I spent. Week trying to learn it and it reduced me to tears on more than one occasion. I’m not a thick or stupid person (I hold a PhD and spent 30 years running businesses) but if “simple maths” isnt your thing then Astro is fiendishly hard.

That’s an interesting comment. If you don’t mind, how did you try to learn and what was the issue?

Did you self-study, online or with a real person?

It’s not a commonly requested Shorebased course but it’s very enjoyable to teach, preferably one-to-one or small group.

I’ve found that regardless of background, some people at first struggle with adding and subtracting day-hour-minute-second, ditto degree-minute-decimal minute. Practice and perseverance generally pays dividend.

It can be rewarding when the penny drops and the student recognises that it’s actually all fairly straightforward.

 

[Frank Holden]

That’s an interesting comment. If you don’t mind, how did you try to learn and what was the issue?

Did you self-study, online or with a real person?

It’s not a commonly requested Shorebased course but it’s very enjoyable to teach, preferably one-to-one or small group.

I’ve found that regardless of background, some people at first struggle with adding and subtracting day-hour-minute-second, ditto degree-minute-decimal minute. Practice and perseverance generally pays dividend.

It can be rewarding when the penny drops and the student recognises that it’s actually all fairly straightforward.

No offence intended to anyone anywhere.
The 'Second Mates Certificate of Competency' required - back in the old fashioned days- 'O Level' maths. Nada Mas.
Too many people get too engrossed in the finer detail. Its a bit like thinking you need to understand the workings of a syncromesh gearbox before you get behind the wheel of a car.
I've lost track of the number of people who have said 'What about Lunars ? I want to do lunars!!'
Ask Captain Lecky about lunars, sigh.
For reasons you don't need to know I had to do a small bit of research on the 'Equation of Time' the other day.
I found this
Equation of time - Wikipedia
I didn't understand a word, OK I understood a few but not many.
Me? Earth's orbit around sun is an ellipse.
It goes faster and then it goes slower 'cos of the area under the curve or something or other.
Don't think I had to know that for any of my tickets.

Oh and also re copyright I wrote a bit around the same time on compass adjustment, published in same mag. Cupla years later found the Launceston, Tasmania Navigation College was printing and handing it out to students. We were not amused.

 

[obmij]

Just want to add to this thread that Astro IS hard. I spent. Week trying to learn it and it reduced me to tears on more than one occasion. I’m not a thick or stupid person (I hold a PhD and spent 30 years running businesses) but if “simple maths” isnt your thing then Astro is fiendishly hard.

I agree with this.

It's a fairly long winded process working up a sight, with a lot of potential failure points within the workings. It wasn't uncommon for me to get completely nonsensical results even when the sights were given to me as I would make a simple fetching and carrying error which would throw everything out. Time would then have to be spent working backwards to discover the culprit. Very frustrating.

That is before getting into the meat and drink of the matter which is the correct handling of the sextant, the bringing down and accurately recording of the sights & correctly identifying the celestial bodies to use.

In an ideal world we would be practicing every day, but I doubt that many do, even when sailing offshore. I think it is pretty good then to be able to eliminate many of the simple failure points by using software. It is then more realistic (and pleasurable) to practice actually using the sextant.

So - if there is ever a need to use in anger, at least you would be able to rely on the sights!

 

[PhillM]

That’s an interesting comment. If you don’t mind, how did you try to learn and what was the issue?

Did you self-study, online or with a real person?

It’s not a commonly requested Shorebased course but it’s very enjoyable to teach, preferably one-to-one or small group.

I’ve found that regardless of background, some people at first struggle with adding and subtracting day-hour-minute-second, ditto degree-minute-decimal minute. Practice and perseverance generally pays dividend.

It can be rewarding when the penny drops and the student recognises that it’s actually all fairly straightforward.

I read a couple of books then took the 5 day RYA Ocean Yachtmaster theory course, in June of this year (I wont name the school because I don’t blame them for my inability). I spent a very frustrating week trying to copy numbers from a board, and trying to keep up with people for whom adding and subtracting time/distance seemed natural (for me it is not - so yes, that was one problem).

The speed at which new information was presented and comprehension assumed plus and lack of basic explanation of WHY we were adding things up didn’t help me either. Add to that a set of confusing forms and acronyms for which I never did get to learn the names or reasons for the letters, and I ended up not really understanding much at all. I asked questions all week and to be fair to the instructor he did try and answer them. But everybody else looked like they understood, so he kept moving on. In private conversations, most of the others were struggling too, but they didn’t want to show ignorance by asking questions (which I found interesting/strange). I never mind looking foolish if by doing so I learn something.

There was a kind of 'Ah ha' moment just before the exam but while I passed it (actually finished 2nd out of the 5 of us taking it and got it right first time) it was because I had learned the 'rote' of following a paper process we had been practicing all week. Having a set of notes on the training almanac and tables also helped. It was very much a case of being trained to take an exam, instead of a proper education in the topic.

Now faced with my own sextant, a real set of sight reduction tables and the almanac, I don't understand what I am doing. I was hoping to be able to do the required Ocean YM sights on the forthcoming ARC but I am not confident. If I get enough time and the skipper can coach me, perhaps I will be able to. But I will only present them if I feel that I fully understand what I am doing and am able to replicate it at will. Mind you, I still need to do Yachtmaster Coastal/Offshore practical exam before taking the YM Ocean, but the opportunity to take the sights on a decent passage seemed like good a way to go. Time will tell.

 

[PhillM]

You may want to look at the book I mentioned in post #4 I found it took me step by step and I've found it very easy.

Thank you, I have got a kindle copy.

 

[capnsensible]

I read a couple of books then took the 5 day RYA Ocean Yachtmaster theory course, in June of this year (I wont name the school because I don’t blame them for my inability). I spent a very frustrating week trying to copy numbers from a board, and trying to keep up with people for whom adding and subtracting time/distance seemed natural (for me it is not - so yes, that was one problem).

The speed at which new information was presented and comprehension assumed plus and lack of basic explanation of WHY we were adding things up didn’t help me either. Add to that a set of confusing forms and acronyms for which I never did get to learn the names or reasons for the letters, and I ended up not really understanding much at all. I asked questions all week and to be fair to the instructor he did try and answer them. But everybody else looked like they understood, so he kept moving on. In private conversations, most of the others were struggling too, but they didn’t want to show ignorance by asking questions (which I found interesting/strange). I never mind looking foolish if by doing so I learn something.

There was a kind of 'Ah ha' moment just before the exam but while I passed it (actually finished 2nd out of the 5 of us taking it and got it right first time) it was because I had learned the 'rote' of following a paper process we had been practicing all week. Having a set of notes on the training almanac and tables also helped. It was very much a case of being trained to take an exam, instead of a proper education in the topic.

Now faced with my own sextant, a real set of sight reduction tables and the almanac, I don't understand what I am doing. I was hoping to be able to do the required Ocean YM sights on the forthcoming ARC but I am not confident. If I get enough time and the skipper can coach me, perhaps I will be able to. But I will only present them if I feel that I fully understand what I am doing and am able to replicate it at will. Mind you, I still need to do Yachtmaster Coastal/Offshore practical exam before taking the YM Ocean, but the opportunity to take the sights on a decent passage seemed like good a way to go. Time will tell.

I've found that it's best not to dwell on the theory of sight reduction at the beginning. By getting students to do practical working through the pro formas it's possible to understand things a bit at a time.

Actually taking and reducing a real sight they have taken, whenever possible, is a big help too.

Everything sailing = practice, practice, practice.,

Edit to add. A transat is great. Northern hemisphere, moving westwards from Greenwich, the easiest of the arithmetic. Adding up and taking away. Doesn't get easier! Each day, things haven't moved much so if you struggle at the beginning, especially when tired and or a bit of mal de mer, it will get easier.

Plus, for morning and afternoon sun sights, if its all going wonky simply bin it and go take a new one!

Enjoy your trip and you have something to fill your time....

 

[jdc]

I've found that it's best not to dwell on the theory of sight reduction at the beginning. By getting students to do practical working through the pro formas it's possible to understand things a bit at a time.

I agree 100%. The important thing for beginners is to get results which actually work! A result only 5 or 10 mins after first picking up a sextant is just so encouraging. For this, some electronics is a boon; the skill he's actually learning is to take a sight and record the time.

Once that's mastered, the beginner can try to convert GHA and Dec (still provided by the program) with the CP's lat and long to a get a calculated altitude, and compare that to the measured altitude - from which Marc St Hilaire's method makes perfect sense, indeed it's obvious. Then digress to making a plotting sheet. Only once happy with these is it worth doing the trivial but pernickety business of interpolation of tabulated values of GHA and Dec to get them at the exact time of the sight.

Doing these step by step, with feedback if they've been done correctly, is so much more effective and encouraging a teaching technique than the traditional method which, imho, conflates too many steps and so tends to confuse beginners.

For those who decry calculators and want a 'manual' method, I ask 'what is that exactly then?' To derive the GHA and Dec are you doing orbital calculations of the earth around the sun to derive them - for which you need to know only the eccentricity of the orbit, the period of the orbit, the time and date of the winter solstice and the date of the perihelion. All else follows, but you have to solve Kepler's trancedental equation and do some fairly stiff trigonometry, so I rather doubt it. Besides, that done, it's still only accurate to about 15', so you have then to add the date and time of the first full moon of the year plus the position of the barycentre of the earth - moon system to apply perturbation theory (remember, the 3 body problem is not soluble by algebraic means) in order to get predictions better than 1'. Does anyone do this at sea? But without these, you don't get much understanding, just learn how to take data from tables.

Also essential for the sight reduction are sine and cosine functions (or maybe haversines), but does anybody derive them (presumably by Newton- - Raphson iteration)? No, you take them from tables. So again 'manual' or 'understanding' means just looking in book - not so different form asking a calculator. Add the corrections for half angles of the sun or moon, and the parallax and the height of eye corrections. Calculate (how?) or just look them up?

So I don't think using a calculator is a cheat, although I can do without for the sun-run-sun method by using pre-computed GHA and Dec, plus simplified 'Air tables', but I favour a calculator, at least for beginners. I wrote this app myself, which it doesn't need connection to the internet once installed. Not saying it's the best, but since I wrote it, I've nobody else to blame if I get lost, so I use it at least.

 

[Frank Holden]

I read a couple of books then took the 5 day RYA Ocean Yachtmaster theory course, in June of this year (I wont name the school because I don’t blame them for my inability). I spent a very frustrating week trying to copy numbers from a board, and trying to keep up with people for whom adding and subtracting time/distance seemed natural (for me it is not - so yes, that was one problem).

The speed at which new information was presented and comprehension assumed plus and lack of basic explanation of WHY we were adding things up didn’t help me either. Add to that a set of confusing forms and acronyms for which I never did get to learn the names or reasons for the letters, and I ended up not really understanding much at all. I asked questions all week and to be fair to the instructor he did try and answer them. But everybody else looked like they understood, so he kept moving on. In private conversations, most of the others were struggling too, but they didn’t want to show ignorance by asking questions (which I found interesting/strange). I never mind looking foolish if by doing so I learn something.
...........

5 Days? Crikey, it took me 5 years. OK the better part of 4 years from going to sea to sitting an exam. Even then much of the theory remained something of a mystery to me for many years.

A couple of points. In that course I wrote over 30 years ago I first described the Air Navigation Tables method. I now reckon 'long hand' is a lot easier for most people to grasp and you don't need as much 'stuff' - the almanac pages downloaded 'on line' from https://thenauticalalmanac.com/TNARegular/2024_Nautical_Almanac.pdf
Scroll down for the daily pages.
You also want a copy of Nories, this is for the log haversines, log cosines, etc.
OK its a big book and costs a few bob but you have already shelled out £££££££ for your sextant.
Use a dedicated sight book, write up each page before you start each day.
One thing I like about the 'longhand' method is it uses plain english, Observed Altitude ( Obs Alt) instead of Ho f'rinstance.

'lack of basic explanation of WHY we were adding things up didn’t help me either.'

Worry about the complicated 'whys' down the track.
Look at things in their parts rather than as a whole.

Why do we have to subtract 'dip' from our Obs Alt.
What is the semi diameter?
What is refraction?
Thats the altitude sorted.
Q? Why do we have to subtract from 90º and use the Zenith Distance?
A. Because it makes the formula easier to work with.

What is the sun's greenwich hour angle and declination?
Its the sun's lat and long but we express it back to front.

What do we need to know to 'reduce the sight'?
The sun's local hour angle and its declination
Our latitude.

In plane trigonometry we use two parts to find a third.
In spherical trig we need three parts to find a fourth

Why do we use the Haversine formula and logarithims?
Because the Haversine of an angle is positive from 0º to 360º
Why logs? because that reduces the workings to three lines of addition.
Oh, OK, except for the Lat~Dec which may involve a single line of subtraction.

I think that covers all the 'whys'.

 

[PhillM]

That’s really good feedback, thank you. Still lots I don’t understand. But I’m sure over time and with practice… but my basic point stands, as a lesiure sailor who does this at weekends and holidays, Celestial Nav is hard. Hard to grasp, hard to learn and I suspect without lots of practice hard to do.

Interestingly, on my course there was a lady from Maiden (she knew how to do it and was there for the certificate), two who had tried and failed before, one professional RAF guy who understood the theory but still needed to practice and me. So it’s not just me who found a five day RYA course tough. Perhaps it needs to be a longer course?

 

[requiem]

It can be rewarding when the penny drops and the student recognises that it’s actually all fairly straightforward.

At various times I had made brief attempts to learn the basics on my own. For some reason they always quickly led to the PZX triangle at which point all the various pieces I was trying to juggle in my mind at the same point ended up falling to the floor.

When I finally did a course there was enough time spent on the basics that things clicked. Much of that was due to resources like Tom Cunliffe's book that had an increased focus on illustration over text. Similarly, when working a sight I still draw simple diagrams as a check against adding when I should subtract and so forth.

I agree with jdc's comments about the "manual method", but I think understanding how the different steps of the rote process fit into the underlying theory may help with the sense of mindlessly following a rote process. I've taken a peek at some practice notes, so will see if I might break them into reasonable blocks of work. Please forgive any sloppiness with the terms, some if it is intentional to avoid pedantic details that might otherwise confuse....

The approach starts with a collection of known values: the celestial object, the current date and time, the height of eye (HE), the index error (IE), the assumed position (AP), and of course the sextant-measured height of the object (Hs).

The approach also includes cleaning up those values to correct for errors and to get to a standard baseline (e.g. GMT). By applying corrections (height of eye, index error, etc) you progress from Hs to Ha (don't worry) and finally Ho, the observed height of the object. Similarly you convert back to GMT time if your sight was recorded in local time.

A second block, that one might equate with longitudes, is calculating the local hour angle (LHA) of the celestial object, which is essentially the Greenwich hour angle (GHA) from the almanac adjusted to measure from your assumed position. ("Hour angle" being a fancy way to refer to longitudinal measurements.) Here is where I sketch the first diagram: a simple circle with a tick to represent Greenwich, another to represent my approximate longitude, and a third for the celestial object's "longitude". The relative positions on the circle of the latter two give me a rough idea of what the LHA should be.

In theoretical terms, the LHA represents the angle at the pole between the meridian of the assumed position and the meridian of the celestial object. Think if it as treating your assumed position as 0° longitude and measuring the object's longitude (i.e. "hour angle") starting from there.

In parallel with that second block is a third, which one might mentally equate with latitudes. The key output is the declination (dec) of the object, which one takes from the almanac and to which any necessary corrections are applied. For the special case of a noon sight I draw a sketch to relate the zenith distance (90-Ho) and the declination; this helps to ensure I perform the proper operation.

In theoretical terms, the latitude of the assumed position corresponds to the side of the navigational triangle running from the pole to our assumed position. Well, you'd take 90° - the AP lat, but you get the concept, and similarly the declination of the celestial object allows one to know the length of the triangle side that runs from it to the pole. This, combined with that angle from the second block above, means you have a rough "side-angle-side" setup for calculating the rest of the triangle.

Finally, having LHA, my assumed latitude, and dec, I can move to the sight reduction tables. Those are what many of the calculations are hidden behind, and the output of the lookup contains: the calculated height (Hc) of the object from the AP, and the azimuth of the object from the AP (Zn). From this information I can plot the azimuth from my AP, and by comparing Ho to Hc I know how far to adjust the position line. (Hi Ho, Hi Ho, it's off to work we go...)

Going back to theory, you've just obtained the values for the missing leg of the navigational triangle and the angle between the pole and the celestial object. The precise azimuth doesn't matter too much, as it would change very little between your assumed position and your actual position.

 

[Frank Holden]

..snip..

For those who decry calculators and want a 'manual' method, I ask 'what is that exactly then?' To derive the GHA and Dec are you doing orbital calculations of the earth around the sun to derive them - for which you need to know only the eccentricity of the orbit, the period of the orbit, the time and date of the winter solstice and the date of the perihelion. All else follows, but you have to solve Kepler's trancedental equation and do some fairly stiff trigonometry, so I rather doubt it. Besides, that done, it's still only accurate to about 15', so you have then to add the date and time of the first full moon of the year plus the position of the barycentre of the earth - moon system to apply perturbation theory (remember, the 3 body problem is not soluble by algebraic means) in order to get predictions better than 1'. ..snip..

Ouch my brain hurts

 

[Buck Turgidson]

I use the iPad version of celestial navigation whenever I take sights. Either before or after I've done the manual calc and plot. It's a great tool for checking your method and maths. Very useful to know quickly that you have done something wrong and the app will show if your sighting technique is adequate or not.