Question on Celestial Navigation

brainstorm

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I enjoy using traditional navigation methods and have mastered using a sextant to do noon sights and sun sights. This year I would like to learn more about doing star sights. I have bought the 2019 Nautical Almanac which gives plenty of info on sun moon and planets and some info on stars. But as far as I can see it does not recommend “selected stars” as AP3270 Volume 1 provides. And I do not understand the tables towards the back.

Can anyone tell me whether I can take star sights and then work out a position line using just the Almanac, or do I need to spend another £32.50 to buy Volume 1 for the one or two occasions when I have a combination of calm seas a clear sky and a clear horizon!

Any advice welcome. I did an RYA refresher course recently but there was very little help on stars.
 

Frank Holden

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brainstorm

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My word the power of this forum!

Burg thanks very much for that link I did not realise you could get these tables on the net now. I will print just the 20 odd pages from a Selected Stars for 50 to 60 degrees North. Presume I should use the older version for epoch ending 2019 this year rather than the new 2020 one.

Frank....not only a helpful reply but a link to your excellent looking publication which will entertain me for the remaining winter nights until I can get afloat again. I know where to come now for any other queries!

Many thanks again
 

Skylark

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Which “tables towards the back” do you not understand?

You can use the Nautical Almanac to obtain a Position Line from the stars. Daily Pages show Aries GHA, then add Star SHA and Dec. Then, follow the Sight Reduction procedure.

The issue is identifying the star. AP3270 Vol 1 does this for you. Use the Table in readiness for the Twilight Observation Period, set sextant altitude, turn to its azimuth and voila. Well worth the £32.50 extra, imho.

The linked W&P star finder also works well. I found one, ex WW2 air navigators, on eBay. Although the Epoch must be almost 80 years ago they still give a reasonable alt and azimuth.
 

BelleSerene

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err hum........
http://thenauticalalmanac.com

You might find everything you need there.

That is really excellent to have for free online! However, the 2019 pages from it are several times the amount of paper in Reed's Astronavigation Tables for the year.
https://www.amazon.co.uk/Reeds-Astr...ro+navigation&qid=1551780348&s=gateway&sr=8-1
And for about half the OP's comparison price of £32.50 for Vol 1 of AP3270, he can buy that second-hand from Amazon.
 

john_morris_uk

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For completeness:

You can take and reduce a star sight to a position line without selected stars... Provided you are confident that you have identified the star correctly, munch through the calcs with its Dec and SHA added to the HA of Aries and the calculation process is similar in many ways doing a sun sight,
 

MM5AHO

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I find the hardest part of star sights to be determining the horizon properly. Needs to be dark enough to see the stars well enough, but not so dark that the horizon is indeterminable. The moon is challenging, but the planets can be an interesting diversion.
 

Porthandbuoy

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I’ve never had much success with star sights taken from the deck of a small yacht. By the time the stars are visible I find the horizon too ill defined and if I ‘lose’ the star in the sextant telescope I sometimes ‘find’ the wrong one, which really screws up the sight.
Venus and Jupiter are often visible much earlier, often even before the sun has set. They can be useful when the sun is low and refraction great.
 
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I got to be marginally competent with sun sights.

But I never managed a star sight even when I had a chance to use a better sextant with the much larger scope. 50 mm x 5 from memory. Just too many ********** stars.

Take the scope out for star sights .Sight the star thru the scope hole, and bring the horizon up to it. Best at dusk and dawn, when you can see the horizon.
 

DownWest

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The all time champions of navigating by the stars were the post WW2 bomber crews especially the Vulcan boys.

They generally nailed it to withing 2 miles at 300 knots.

The SR 71s had a star scope built in, as pre GPS; One guy found his was inoperative, but thought he would wing it. Missed his turn by half a state. Bit faster than 300kts mind.
 

maxi77

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It is many years since I did astro for real. I think my last fix was in the middle of the Bay in 1971 with a periscope artificial horizon sextant, just after I had done my Ocean Navigation certificate using bottom contour navigation. Even so the key to a good fix is preparation. You need to know what you will be taking a sight of, not to difficult for the sun but vital for stars/planets where you really need to know expected altitude and azimuth. Fill out the sight form in advance with what you know before the sight is taken. Make sure your time piece is accurate or the error is known. If you can have a note taker. If you have a reduction spreadsheet ot software use it, no point in making silly arithmetic errors when you can avoid it. Do the paper sight reduction ashore where you can understand what you are doing and learn about the mistakes that can be made. Finally take a GPS position at the fix time so you can see your errors and learn from them. Enjoy
 

weustace

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The all time champions of navigating by the stars were the post WW2 bomber crews especially the Vulcan boys.

They generally nailed it to withing 2 miles at 300 knots.


My grandfather flew the Avro Lincoln in the early 50s. He graduated to command of the aircraft and was granted his temporary commission on his 18th birthday; his navigator was a much older man who unfortunately was rather prone to error. Apparently he was ok during the daytime, it being difficult to get the wrong star, but my grandfather has frequently recounted one mishap in which they were placed some 800nm adrift over the Indian ocean and found themselves unexpectedly over mountains instead of at sea. Given they were cruising at 3000-5000 feet, this was an unfortunate situation fortunately saved by the radio operator, who was able to get an RDF fix. The Air Navigation Tables at the time had a picture of an ancient navigator on the front with the caption "Man is Not Lost": grandfather felt that this did not apply in all cases.
 

maxi77

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My grandfather flew the Avro Lincoln in the early 50s. He graduated to command of the aircraft and was granted his temporary commission on his 18th birthday; his navigator was a much older man who unfortunately was rather prone to error. Apparently he was ok during the daytime, it being difficult to get the wrong star, but my grandfather has frequently recounted one mishap in which they were placed some 800nm adrift over the Indian ocean and found themselves unexpectedly over mountains instead of at sea. Given they were cruising at 3000-5000 feet, this was an unfortunate situation fortunately saved by the radio operator, who was able to get an RDF fix. The Air Navigation Tables at the time had a picture of an ancient navigator on the front with the caption "Man is Not Lost": grandfather felt that this did not apply in all cases.

My big astro failure was also in the Indian ocean, we were off Beira, Mozambique and I did evening stars as usual under the supervision of the Jimmy. It was only after the fix put us in the Atlantic off Angola that we realised there was a time error, and investigation found the deckwatch had been allowed to stop , been restarted and set approximately to the correct time. Time error should be reasonable to discover as your latitude is still the same but longitude is shifted.
 

Barnacle Bill

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Going to put a post here because anyone looking at this thread, and wondering how to do Astro, might be interested in this:

Reeds Ocean Handbook (which has lots of other information about Ocean sailing too) has a section on Astro Navigation which gives a 'step-by-step' guide to sight reduction, using only the tables in The Nautical Almanac (i.e. you don't need the Air Tables - there is a perfectly good sight reduction table in The Nautical Almanac).

Nowadays almost everyone uses GPS, so the main use for Astro is a fall-back for position fixing - and this method is good for that.
 
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