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Celestial navigation

Old 21st Jul 2014, 07:59
  #21 (permalink)  
 
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For what it is worth in 1967 Qantas still had navigators on 707's doing long over the water sectors like Sydney Honolulu.
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Old 21st Jul 2014, 14:50
  #22 (permalink)  
 
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Thanks for that information.
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Old 21st Jul 2014, 15:06
  #23 (permalink)  
 
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This is a short clip about a flight crew going through the use of an astro-compass. Sorry, there's only 1 video, but there's two being shown here in the thread
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Old 21st Jul 2014, 19:45
  #24 (permalink)  
 
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Criticalmass, thanks very much, great info.

Yes 5 miles is negligible for a long sea voyage at ship speeds on a very big ocean.
As you said celestial nav for aviation had to be replaced due to a number of factors as time and technology moved on.

The WW2 eg I mentioned before, night nav over a blacked out Europe would rely heavily on astronav with a possible 5-10nm radius of error for airborne fixes as opposed to approx 5nm at best when stationary on the ground at a known location. With only these fixes usually avail to update the airplot and all the compounding errors caused by varying winds, accuracy of flying heading and airspeed etc these would of cause often cause very large errors in establishing a ground position and thus led to very, very, poor bombing accuracy.(hence "Area Bombing" as a result).
Even 1-3 nm is a huge amount when trying to hit a small cluster of buildings in a large city, like a factory complex or a small village for eg. A very big problem in those days before other methods were developed to improve position fixing at night in bad weather.

I will let all you knowledgeable "old sailors" finish this interesting discussion . Great to see this "art and science" is being kept alive by at least a few around the world.
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Old 22nd Jul 2014, 05:48
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Danger

When I retired from the USAF in 1988 flying KC 135s we were still using celestial. We had an INS, but with only one it needed backup. We also had a Doppler, but over water they weren't too reliable either. Our navy's practiced cel on almost every flight.
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Old 22nd Jul 2014, 06:02
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Nice explanation video there.

Which reminds me, does anyone know where I can get mine fixed. The latitude knob snapped off. It survived WW2 according to its Duxford 1944 service stamp, but broke when my then 3yo pulled it off the table...
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Old 22nd Jul 2014, 07:24
  #27 (permalink)  
 
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For the math(s), most yacht-master examiners are happy with the candidate using a calculator. It's only a few of the RYA fossils who remember teaching Nelson who insist on the longhand version. I used my wife's old Texas TI82 with a celestial navigation programme at first, but then I loaded the AstroNav app onto my iPhone. When I did my yacht-master, the examiner was happy with it. Astro Nav will allow you to input your chosen celestial bodies and does everything for you. Although it does give you the option of inputing your assumed position from the GPS! . Furthermore, in extremis you can use your iPhone as the sextant utilizing the accelerometers. It's not going to be as accurate as a real sextant, but I have achieved a fix within 15 miles of my actual position on it. Asto Nav also has a very good tutorial. For identifying the celestial bodies, the Nightsky app is useful.

I write for a sailing magazine and have always pointed out the potential for satellite navigation systems to be unreliable and have advocated that yachties do need to keep up with their celestial navigation.
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Old 22nd Jul 2014, 22:12
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They still teach it...

I'm a professional mariner, and amateur pilot, and I can assure you that celestial navigation is still being taught at maritime colleges. Gues the maritime world is a couble of decades behind the aviation industry, especialy when it comes to education. (The whole human factors thing is just about catching on too, to get your masters licence you now need to do a 'bridge resource management' course).

From a large stable ship, with a sextant that hasn't been dropped too often, it is quite posible to get within 2NM of your true position if you manage to get 6 or 7 stars 'shot' in the twilight. Using the sun with 3 hours of DR between your LOPs is obviously a lot less precise.

I never had the chance to use an aviation sextant with an artificial horizon, but I would imagine the maritime model would be more accurate. With the big disadvantage that you have to wait for twilight to get a position using stars.

If you don't wan to use an electronic calculator or computer for your calculations, but don't have the patience to learn the old fashioned way you can use volume 1 of the 'Sight Reduction Tables for Air Navigation'. With some practice you can plan, shoot and calculate 7 stars in about 20 minutes (although when I was a cadet, my chief mate considered them cheating ).


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Old 23rd Jul 2014, 01:08
  #29 (permalink)  
 
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Stellarium

Another useful celestial application is Stellarium. Is free open-source and available for Windows, Apple and Linux. Stellarium
I believe app version is also available for Androids. Interested to know if anyone has compared it to Nightsky.
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Old 24th Aug 2014, 20:57
  #30 (permalink)  
 
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Celestial - Airborne

But then airborne celestial is quite different from maritime in practice.

The sextant is different, all calculations are done beforehand rather than after the shooting, and additional corrections need to be made for speed, altitude, coriolis, course deviations etc. It's actually quite more complex. But very satisfactory once accomplished.

best performance to be expected is 2 nm, but 5 - 10 nm is more realistic. Doesn't sound great compared to GPS, but it gets you to that island airfield out in the pacific. I have recently achieved 5 nm in a self-restored WW2 bubble sextant while in a microlight aircraft.

I have a few of these devices and learnt the skill recently. Would be willing to help out anyone interested.

Eric
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Old 3rd Sep 2014, 06:59
  #31 (permalink)  
 
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I was a Royal Navy Navigation Officer, so was taught astro and used it at sea. Really learned how to do it as a yachtsman when delivering a boat from Manila to HK, when the electronics all failed, and I had to revert to astro. Also had problems with electronics during a Fastnet race, and astro was the only way to find out where we were.

Best book I ever read on the topic was "Celestial Navigation for Yachtsmen" by Mary Blewitt - far better than anything the RN produced. I'd pre-work the stars using the Air Tables to identify them before shooting, and find the planets using a star finder (plastic sheets shaped for chosen latitude). Calculating the position lines was done with an ordinary scientific calculator.

Haven't done it for years, but not difficult to learn. And very satisfying.
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Old 3rd Sep 2014, 07:24
  #32 (permalink)  
 
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Thumbs up

Mary Blewitt's book is excellent!! Used it for years after learning astro for the Flt Nav licence then needing to convert the skill to the sea.

G'day
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Old 3rd Sep 2014, 07:30
  #33 (permalink)  
 
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Another vote for Mary Blewitt's excellent book. The lady is long gone now, but the book is still widely available. Makes it very easy to understand.
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Old 10th Sep 2014, 01:45
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I dove in the subject as well. I am pursuing the FAA flight navigator certificate. I purchased an A12 bubble sextant on ebay and a Polhemus celestial flight computer.

Aircraft Bubble Sextant Link A 12 100 Reconditioned and Ready for Use | eBay

The sextant I received from this genlteman is in perfect condition with all the parts. You won't find a better sextant than that. There are many out there but be careful, a lot of them don't have the bubble or are just simply missing parts. The Polhemus flight computer is similar to an E6B but designed specifically for celestial navigation. It allows you to obtain essentially almost all your corrections by setting your course, latitude and estimated groundspeed and this without having to open one book. On the other side of it, you can use it for plotting your line of positions. It makes celestial navigation so much easier.

You will still need the Air Almanac (not the one published by UK - it's missing the navigational data) and the H.O 249 sight reduction tables.

Keep in mind that celestial navigation for aviation is slightly different than maritime. The concept is obviously the same but the technique is I would say very much different.
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Old 10th Sep 2014, 10:12
  #35 (permalink)  
 
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What a great thread... Thanks!!
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Old 10th Sep 2014, 22:05
  #36 (permalink)  
 
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OzDork, don't knock your plastic Davis sextant, I carry one on my boat. Get a copy of "astronavigation for yachtsmen", it covers what you need to know.

Personally, a ten to fifteen mile error circle is pretty good from the deck of a small yacht in rough weather and a Davis sextant is plenty good enough for that purpose.

You can use tables or buy a navigation computer and there is probably an App for it anyway.


If GPS vanished tomorrow we would be right back to "proper" navigation and pilotage with Sextant and hand bearing compass, so its worth keeping up those skills, even just against total electrical failure or the iPhone falling overboard.

The things I treasure are a couple of the very old sailing guides for Bass Strait that are no longer in print. They contain vast amounts of hard won information that is no longer considered relevant today. For example if caught in a Westerly gale in Bass Strait there is a patch of safe water behind the bluff at Barwon heads called in the old days "the bosom of Abraham". I've also used them to sail from Port Albert to Port Welshpool via "the cattle crossing" - through a maze of channels, avoiding the open sea.
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Old 27th Sep 2014, 17:04
  #37 (permalink)  
 
Join Date: Oct 2006
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I made a quick little video of the astro-compass. It's super easy to use. You can find them for under $100 on eBay. All you need is a current Air Almanac.

Astro-Compass - YouTube
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Old 28th Sep 2014, 05:50
  #38 (permalink)  
 
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I'm a NSW based Master Mariner (and PPL hence the affiliation with PPRuNe), willing to meet up with anyone locally and introduce them to sextants and celestial nav. Developments are still continuing in the celestial world (whole horizon mirror sextants etc), and it is still an examined subject for professional seafarers.
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Old 28th Sep 2014, 15:14
  #39 (permalink)  
 
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@L'Aviateur: I would like to take you up on that. See pm.
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