Celestial navigation tables

[tane]

direction is Azimuth of the body (star, moon, sun,...), corrected Alt. greater than Hc in tables: towards body, smaller: away. Very easy ("GOAT - greater observed altitude towards")

Of course it increases pleasure of celestial nav, if you know the meanings of LHA, GHA, Declination,... - but for sucessful finding your position this knowledge is superfluous. Skilled sight-taking is more conducive to your precision than if you could do all the spherical trigonometry & not use HO 249/Selected Stars.

 

[Markku_from_Finland]

Ok, thanks. Starts to make sense now.

 

[tane]

I cannot recommend Mary Blewitt's book highly enough. Pretty sure there is at least a Swedish version, if not a Finnish one (supposedly youall Finns speak Swedish too, no? - [if you taciturn people speak at all ;-)])

 

[Markku_from_Finland]

Any educated Finn should be able to read Swedish, but in practice, some people seem to woefully ignore the plentiful school tuition... I read Swedish, however.

 

[sledracr]

In this day and age of cheap little GPS sets, there is no need to "develop" anything new for celestial navigation. 

This.  

Plus, if you want a backup, for about 20 bucks you can get an "HP-41" app for your phone, and with the nav-pack software have push-button sight-reduction without tables.

 

[Jud - s/v Sputnik]

This.  

Plus, if you want a backup, for about 20 bucks you can get an "HP-41" app for your phone, and with the nav-pack software have push-button sight-reduction without tables.

What do you mean by “nav-pack software”?

 

[sledracr]

What do you mean by “nav-pack software”?

HP produced add-on modules (or "packs") for the HP-41 for a variety of topics (math, engineering, etc.)  The nav-pack added a whole gamut of functionality for navigation



Toward the end of the pre-GPS era, that's all I carried: an HP-41 with the nav-pack and some spare batteries, and my sextant.  MUCH easier than carrying around the books (nautical almanac, one or more volumes of HO-249, etc).   OK, I still carried around a copy of HO-208 just as a backup, it's an easy (but less precise) all-in-one reference.

The HP-41 has been out of production for decades, but from (at least the) apple app-store you can get a simulator for about 10 bucks.  Does everything the HP-41 did, on your phone (and actually quite bit faster).  For about another 10 bucks you can import the "nav-pack" software and be off and running.

i41CX on the App Store (apple.com)

For a sight reduction, you basically enter your DR longitude, date and time, eye-height, sextant reading and body.  Press the button, it gives you "a" (altitude intercept, toward or away) and "Zn" (azimuth).  Easy.



As precise as doing it by hand from the tables?  No.  But it only takes about 30 seconds once you have the sight taken.

 

[tane]

I guess all the entering as at least as error-prone as looking up the numbers in the NA & HO249 with anadded disadvantage: the numbers-written down-can easily be rechecked. Plotting-errors: likelihood stays the same.

(...& in my youthful arrogance I always thought the calculators were for people with shaky primary-school-maths...)

 

[LB 15]

I have developed a computer program to calculate the line of position (LOP) as a function of the latitude of the observer, and the altitude and parameters of the star. The output is the Greenwhich hour angle of the observer.

Is anybody interested in this kind of stuff or is this useful? I can very easily produce the tables for the main sailing stars and post them to this forum, if you find them useful.

View attachment 510776

A few years ago one of my ex students told me he had developed a sight reduction app for smartphones. I don't think he understood when i likened it to making a wrist watch with a sundial on it.

 

[Markku_from_Finland]

I think you might use tables, forms & sextant when the power is out. Or when the GPS signal is distorted... maybe distorted GPS + functioning phone is the niche for your student.

 

[Markku_from_Finland]

I wonder how lone sailors (like athletes) found their position before the GPS. Sure they couldn't do DR 24h. So maybe they used some initial trigonometry to get the DR coordinates for the charts?

 

[LB 15]

I think you might use tables, forms & sextant when the power is out. Or when the GPS signal is distorted... maybe distorted GPS + functioning phone is the niche for your student.

Oddly enough in the training world we have seen a resurgence in people wanting to learn Celestial navigation in the last few years. It is still required in the Ocean syllabus, but it is more hobbyists than those looking for a qualification that are doing the training. And of course there are the doomsayers that fear the forthcoming zombie apocalypse will cause every satellite to fall from the sky.

 

[Markku_from_Finland]

Oddly enough in the training world we have seen a resurgence in people wanting to learn Celestial navigation in the last few years. It is still required in the Ocean syllabus, but it is more hobbyists than those looking for a qualification that are doing the training. And of course there are the doomsayers that fear the forthcoming zombie apocalypse will cause every satellite to fall from the sky.

There's a certain intellectual appeal to the topic and the stars are beautiful.

 

[Schakel]

There's a certain intellectual appeal to the topic and the stars are beautiful.

Easy for you to say, we in the Netherlands are blinded from the stars. 
There is so much light at night from the highways, citylights and greenhouses, it's hardly impossible to see a star.

But in Finland that's different. Sailing over here is more like driving bumpercars.
Different in Finland as well:  land of a thousands lakes. 187.888 according to Google.

 

[Foolish]

A few years ago one of my ex students told me he had developed a sight reduction app for smartphones. I don't think he understood when i likened it to making a wrist watch with a sundial on it.

15 years ago I got a sextant for Christmas. After reading through 5 books I still couldn't figure out how to use the damn thing. So the only solution was to write my own booklet.  You can download it for free here: Astro Navigation: All you need to navigate by the Sun. (backbearing.com)

But since the day I wrote that booklet I've never used my sextant.  There is a reason God invented GPS.

 

[El Borracho]

When I carried a sextant for backup for the GPS apocalypse the only other thing was the current almanac. Has all the sight reduction stuff in the back. So add pencil and paper and one has everything necessary.

 

[sledracr]

Plotting-errors: likelihood stays the same.

Yeah.... in my experience, plotting errors are far more likely to be the cause of a crappy position than the table-lookups.  There are so many things that have to be "just right" (starting with the longitude scale) for the resulting LOP to be valid.

 

[tane]

I wonder how lone sailors (like athletes) found their position before the GPS. Sure they couldn't do DR 24h. So maybe they used some initial trigonometry to get the DR coordinates for the charts?

1. the singlehander very arely sleeps 24h nonstop

2. with a steady wind under windvane or autopilot the course is pretty much constant, & the log gives you the miles the boat has travelled. Bingo! Your DR position. Then you get a starfix, you see how much the DR was out, & the game starts from zero.

3 &1/3 rtw - & never a trigonometric calculation used (& not because of GPS on the last 1 1/3!)

(Markku, I think you are making rocket sience out of riding-a-bicycle...

 

[Markku_from_Finland]

1. the singlehander very arely sleeps 24h nonstop

2. with a steady wind under windvane or autopilot the course is pretty much constant, & the log gives you the miles the boat has travelled. Bingo! Your DR position. Then you get a starfix, you see how much the DR was out, & the game starts from zero.

3 &1/3 rtw - & never a trigonometric calculation used (& not because of GPS on the last 1 1/3!)

(Markku, I think you are making rocket sience out of riding-a-bicycle...

Yeah, I get it. There's really no need for my tables.

I humbly thank you for an interesting discussion!

 

[sledracr]

There's a certain intellectual appeal to the topic and the stars are beautiful.

Agreed!

And while we're inventing things, I'll add my contribution to the hive-mind... probably something that is obvious to many, but I felt ever-so-clever.

I wrestled with capturing time-of-sight (off a watch or chronometer) while on deck, having a sextant in one hand and holding onto the boat with another.

"back in the day", I discovered that a small tape recorder (hanging on a lanyard around my neck) solved that problem - I'd start a recording at a known point in time, then go on deck and just talk to the recording.

     "recording started at nineteen-oh-three GMT"
     "Arcturus, sight one, mark"
     "sextant reading 27 degrees 14.1 minutes"
     "Arcturus, sight two, mark"

Etc.   Easy to do

Then, at the chart table, I could determine the exact second that I took each sight, from the recording, and had the sextant reading for each sight, without having to juggle stopwatch, note-pad, etc.  I found it helped me get better sights, *and* have better info when working them later.

These days I can do the same thing by starting a voice-recording on my phone, and when playing it back the digital counter on the phone shows me how many seconds into the recording I am at each point in the process.  Works for me....