You can also do the trigonometry yourself on any simple student calculator that will allow you to generate the lines of position for plotting each star. The Nautical Almanac gives you the equations, and it is easy to make up your own worksheet to guide you through the process. See below*

The problem is all that ephemeral (constantly changing) stellar position data which you need to to go into the sight reduction tables, the Greenwich Hour Angle and Declination for every celestial body for every moment in time. The Nautical Almanac gives you that for a year, but it is also available as a dataset, centuries of ephemeral data on one CD. But to view that data, you need beaucoup tech.

The whole point of celestial is that you can divorce yourself from the internet, electricity, and all the electronic gadgets and com links to the outside world. For the price of one good sextant (and a lot less aggravation), you can buy plenty of redundancy, 4 robust, waterproof, battery-powered pocket GPS units, but you will now become dependent on the government to operate the satellites for you, and I’m enough of a Libertarian/Luddite to feel very uncomfortable about that. Besides, I only had to learn CelNav once. I don’t need to learn a new software or technology, something which gives me no collateral understanding of the astronomy, math, geography, or cartography involved, every six months. The damn engineers are always fucking with your tools. That’s how they earn a living.

My only “backup” is an 18 year old battery powered waterproof pocket GPS I keep in my briefcase if I should accidentally drop my sextant over the side. BTW, that GPS, a Garmin 45XL, comes with a 62 page instruction manual that takes up more space in my briefcase than my Almanac. I still haven’t read it all.

*If properly reformatted, this will all fit neatly on one 8 1/2 x 11 sheet of notebook paper.

INPUT DATA
Ho = ___________

DEC = __________ GHA =______________ LAT = ___________ LON = ___________

INTERMEDIATE VALUES
LHA = GHA + LON = ___________ (Add 360 until 0

Cos LHA = _________________

Cos DEC = ___________ Cos DEC x Cos LHA = ________________ = C

Cos LAT = ___________, Sin LAT = __________, Sin DEC = _____________ = S

INTERCEPT CALCULATION
Hc = INVsin ( S x Sin Lat + C x Cos Lat )

Hc = INVsin ( __________ x _________ + __________ x ____________)

Hc = INVsin ( ______________________ + ________________________)

Hc = INVsin (__________________________________________________)

Hc = ____________________________________ Cos Hc = ______________

Intercept = Ho - Hc = ______________

Hc > Ho, the intercept is drawn AWAY from celestial body
Ho > Hc, the intercept is drawn TOWARD the celestial body.

AZIMUTH CALCULATION
X = ( S x Cos Lat – C x Sin Lat ) / Cos Hc

X = ( _________ x ________ – _______ x ________ ) / Cos Hc

X = ( _______________________ – ____________________ ) / Cos Hc

X = ( _______________________________________________ ) / _____________

X = ________________________________________________

If X is greater than +1 or less than -1 (due to truncation error), just, reset it to +1 or -1.

A = INVcos ( X ) = INVcos (_______________) = ___________________

If LHA > 180 degrees, then Azimuth Z = A
Otherwise, Z = 360- A

First, shouldn’t it be easy to plug several sextant sightings into a simple program on an HP or TI calculator and get your plot? It seems to me that after the sighting the rest of the procedure is mechanical.

Second, in the event of a boat being swamped I can see the possibility there was no electrical power, no batteries, no nothing. In that case the sextant and book might be invaluable. The down side is that there may be no navigating with no power. I believe that waterproof Marine Band handhelds are common, though.

I’d be a rich man if I could sell all my toys made obsolete by new technology for 10 cents on the dollar. Well, not rich, but one with some money and a lot more room.

Nice story. Thanks for the post.

You had to sign up ahead of time to use it, and have all your calculations algebraically laid out in powers of ten format so you could slide in, do your crunching, and get out. There was always a line of people waiting to use it, and if you screwed up your calculation you wouldn’t get a chance to debug it on the machine.

There were rumors that somewhere in the computer center there was a CRT/keyboard interface to the IBM 360, but I never saw it. The engineers probably had armed guards around it. I submitted my card decks and got my printouts the next day, just like everybody else. This was in ’71.

I never saw a remote monitor or used a text editor until I started my job as a programmer in 1979.

That was back when a decent HP was several hundred dollars. I still have and extensively use my HP 41C, (although the card reader mechanism literally dissolved. Wrong kind of rubber on the drive wheels). I got it as a goodie doing rocket work for someone. I could never have afforded one in a million years.

My first electronic calculator was in high school chemistry class, a desktop with nixie tubes. First one I had seen that could field scientific notation, and I had fun trying to figure out stuff like how many protons you’d have to put side by side to reach the Andromeda Galaxy.

http://www.celestaire.com/Astra-IIIB/Astra-IIIB-with-Trad-Mirror.html

I bought mine in Sausalito.

I never could afford one of them bamboo K&E beauties when I was in school (the kind you wore on your belt in a leather scabbard, like a sword. The pocket calculator had not been invented when I was a science/math student. I had a cheap aluminum Pickett I picked up in the Navy (I still have it, too.)

I used to be really good with it, too, but this Luddite draws the line right there.

I still have one of the old slide rules, the good precision ones they made from bamboo. I have some cheap ones too, including a circular one. I don’t remember anything about how to use one now.