Celestial navigation

[tonyran]

Thelast thread on celestial navigation seemed to unravel somewhere. For selecting stars for star sights and finding bearing and altitude you need Sight Reduction Tables for Air Navigation (AP 3270) Vols 1,2,3. (If you didnt know that already) Good luck.

 

[snowleopard]

For stars, only vol 1. The problem with that is that unlike vols 2 & 3 for sun, moon and planets which last for ever, vol 1 has to be replaced every 10 years and it's not cheap.

Sight reduction tables aren't the only way of doing astro nav. For those interested in it for its own sake rather than a backup for the GPS, why not try the Haversine Formula? It takes only a little longer.

 

[iangrant]

Tony - yes sorry the thread did unravel as you say.

I'm getting there - now starting to think about the tables as I'm getting to that bit in the books. The declination penny had dropped now!


Ian

 

[alex_rogers]

I've also found the book -

The Complete On-Board Celestial Navigator by George C. Bennett

- very good.

It incorporates reduction tables and an almanac for stars, planets, moon and sun. By reducing the accuracy of these tables to 1 minute, they can all fit in one book, and for an ocean passage, this loss in accuracy is irrelavant.

I used this on an Atlantic crossing and it was my favoured method by the end - apart from using a Celesticomp calculator ;-) - but that's cheating.

 

[Guest]

Post deleted by danfoley

 

[RPC]

An easy solution to tables, and also remembering how to do the calcs, is to use an astro computer (a preprogrammed calculater).

A problem with earlier models was loss of the program if the batteries went flat, this is now solved with the latest models. These calculaters have all the tables (perpetual almanac) plus all the software to solve a sight easily. Although they are not cheap they certainly are great for distance cruising.

I have used astro calculators for years and think they are a good solution to keeping up to date tables as well as removing some of the risk of making errors.

You can see a few links to such calculators here, I have recently researched astro calculators and there are not many around anymore but the Starpath one looks good.
http://www.onpassage.com/Training/Training.htm

I do not have any commercial interest in any of these, I used to use the Merlin II, no longer available.

 

[snowleopard]

Sight reduction tables also use the Marcq St Hilaire method. The term refers to using the difference between assumed and calculated positions to reduce the plotting of sights to something that can be done on a piece of paper or a chart. This difference, the intercept, is calculated by tables, Haversine formula or computer.

 

[Talbot]

[ QUOTE ]
An easy solution to tables, and also remembering how to do the calcs, is to use an astro computer (a preprogrammed calculater).

[/ QUOTE ]

For me the whole point about being proficient with astro is to have a method of identifying where I am if I have an electrical failure, or my laptop dies, or USA shut down GPS etc.

relying on a hand held calculator does not meet these requirements!

 

[tome]

Fair comment, but your alternative is paper tables, non? For me it's not worth the buggeration factor.

 

[MASH]

Talbot, its a frequently mentioned fear that Uncle Sam might "turn off" GPS. This fear is completely unfounded. He won't. He can't.

Several years ago now GPS became accepted as a primary navigation aid for commercial aircraft amongst others and the US Govt made a commitment that this being the case it no longer had the option of turning the system off. To do so now would deprive a large proportion of the airliners currently airborne of their nav info which is clearly unacceptable, along with global trucking and other vehicular systems, law enforcement "tags" etc. Aircraft fly approaches to 200'agl, maybe below, on GPS alone in some countries (inc USA) so much increase in jitter, let alone a swith-off, would be instantly hazarding lives. It simply isn't an option.

But then, eggs and baskets...

 

[trouville]

Im more worried about the GPS just going off line with a power problem!Haveing said that as my passages are rearly more than 24hrs its only a theoretical problem!

I bought a sharp calculater with a program for resolving astro in 1985 and its was still running on the origanal batterys in i996! Admitedly i dident use it more than 20 times a year to show i could find my way with a sextent!!(more or less)

The link posted at the starts great! Now all i have to do is buy another sextant and try to use it,Its quite difficult or was for me to get a good possition and the exact time!! I honestly never got a possition that was as precise as my then loran C and now GPS, Perhaps it was becouse i dident have to??

I hadent thought about aircraft!! Then perhaps it wont be switched off,but with Bush can we be sure??

Now ill sail amonst the rock lined channels with less worry about the GPS just going off!! Thanks!!