Hello,

Delighted to be accepted as a member of this exclusive forum.

I have been boating for more than 45 years and have decided it is high time I learned the art of Celestial Navigation. Having studied 2 books Tom Cunliffe and Mary Blewitt I feel I have a reasonable understanding of the subject, however both books use tables (AP3270) to determine the Intercept and to continue my studies I would like to be able to calculate Zn and Hc directly using a scientific calculator.

I turned to youtube and found Cram Daily PH

Formula for missing side

cos xz = cos px  cos pz  +  sin px sin pz cos P

After much ado I discovered how to use this formula and arrived at the same answer as the example given.

Formula for angle

cos Z = - cos P cos X + sin P sin X cos Px

Not attempted this formula yet 

I then discovered Chris Nolan

Formula for side

sin Hc = sin L sin D + cos L cos D cos LHA

Due to my success with the previous formula I had little trouble with this arriving at a very similar answer to the example given although I tried it to a different number of decimal places on the calculator which reveals quite different results

Chris Nolans formula for Z

cos z = sin D - sin L x sin Hc / cos L x cos Hc

Not tried this yet

I am at a very early stage regarding studying this direct method and hope to learn more from this forum.

If anyone is interested I can post my exact workings for the above

I do have a specific question but I guess this is enough of my ramblings for now.

Mike

I'd like to set up a UPS based on a distance of 60 seconds and am having a difficult time of it.   It's probably because I've been working at it too long and it's late!

Here are my assumptions;

- The scale for minutes in the middle of the UPS can also be considered to be just 60 seconds.
- In setting the correct meridian distance for say, N 35°, is done exactly as one would set the meridian distance for 35°.

Any ideas about this?

Thanks,

Craig

Dear member of the forum,
Does anybody know where in the USA I can send my sextant mirrors to be re-silvered?
My mirrors are starting to look a little sad.
Regards,
Steamburn

I've just added a new page where you can get everything you need for 2024 Celestial Navigation.


Click here- Everything you need for 2024


Almanacs
2024 Nautical Almanac- regular format
2024 Nautical Almanac- compact format

2024 Sun only- regular format
2024 Sun only- compact format


Sight reduction
PUB. NO. 249 (download individual Latitudes or Volumes) (Vol 1 courtesy of Celestaire) Epoch 2025
PUB. NO. 249 (download individual Latitudes or Volumes) (Vol 1 courtesy of Celestaire) Epoch 2020
PUB. NO. 229 (download individual volumes)

Stars
2024 Stars- SHA & Declination


Corrections
Increments & Corrections Table (yellow pages)
Increments & Corrections Sun only on 2 pages

ALTITUDE CORRECTION TABLES 10°--90°—SUN,STARS,PLANETS
Altitude Correction Tables for the Moon
Polaris- Correction for (Q) 2024


Conversion of Arc to Time
Meridian Passage and Declination of the Sun at 12 h UT
(from The Air Almanac 2024)
Equation of Time curve for the Sun


Astronomical Phenomena


Day of week, Week Number and Day of Year for 2024
ECLIPSES- Solar and Lunar- 2024
Visibility of Planets, Moon phases and Select Stars
(from The Air Almanac)
Moon Phases for 2023 in graphic form (GMT/UTC time based)
WORLD MAP OF TIME ZONES


The USNO hasn't yet released the Astronomical Phenomena for the year 2024 in pdf

I'm at a loss to understand how to calculate LHA while sailing in Eastern longitudes.

What I know;

LHA in Eastern longitudes=  GHA + ApL (Assumed position longitude) (minus 360° if necessary)


Example;

Date-  November 25, 2022
GMT- 10:10:59

ApL=  E 025° 45'

GHA= 336° 00.7'

LHA=  336° 00.7' + 25° 45'= 361°45.7' - 360° = 1° 45.7'

But, here's the confusion, LHA in Eastern longitudes is supposed to be rounded up or something like that and I'm not really sure if it is supposed to be rounded up.  Information on the web is vague and not explained well enough making too many assumptions.  Another possibility is that very few who speak English are sailing, doing CN, in the Eastern hemisphere.

So, my estimate to solve the problem is simply this (tell me if I'm wrong)

Eastern longitudes, LHA= GHA (whole degree's) + ApL (whole degrees) + 1

The problem above could be easily solved like this-  LHA= 336° + 25° + 1° (minus 360°) = 2°

Any ideas about this?

Gentlemen, 

maybe something of an interest for you. I  kinda wrote a formula  which  maybe  useful.  MAybe;>  It can  be used to get a running  fix from bow  and beam relative bearings. It is well-known  procedure.  But  to speed up  calculations,   there are so-called method  of double angles and 0.7, and also distance travels equalls distance off.  Plus a few so-called special  angles , like 36 deg  bearing1 and 69 deg.  bearing 2.  In the last,  particular case distance travelled is equal  distance oiff the beam to  the object you are  taking bearing on.

Anyway, instead of using  just a few angles  why not  to use any angle at the first  bearing  and calculate what  angle should be  at the second bearing  if  you want  to  have distance travelled between bearings to  be equal  to  distance offf beam of that specific  object you took  bearings at.

a very simple drrawing is following.( see attachment).

Again,  nothin  revolutionary,  just maybe helpful.  Thank  you

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Hi
 
I'm interested in the history of star finder models as an aid to celestial navigation and have a small selection of plan models (list below). My favourite is the Italian Sferoscopio del Pino (image enclosed). Earliest found to date by Rude 1921 leading to the 2102-x models, the 2102-D and British Admiralty NP323 still current.
 
I've recently extended to researching the celestial starfinder globes which predate the plan models  by some margin into the 19thC. Russian and Chinese models made up until the 70s at least come up on eBay. Freiberger also still offer one new. Image of my Russian 1978 example shown.
 
Although there are plenty of resources describing current use of the plan models, notably the 2102-D with David Burch's 'The Star Finder Book' recently into a 3rd edition 2019, have found no reports of the globes being used for navigation, past or present. The globes also have many more stars than the almanac tabulates (the Russian has 160, almanacs typically 57) and unclear how useful these extra stars would be without supporting tables.
 
Can anyone comment on how widely used the globes were or are being used.
 
Thanks.
 
David

Star finder models owned.
2102-B
Sferoscopio del Pino 1971 facsimiles of the 1937+ model (inserts in pocket of book 'La Navigazioni Astronomica' by Mario Sacchetti (1971) to support exercises)
USAF CP-300/U
2102-D vintage and current Weems and Plath
British Admiralty current NP323
Russian celestial star finder globe model 3Г 6.6 inches diameter.

April 30, 2022

Here is a link to a popular and reputable supplier of celestial navigation equipment having a sale on the simple but remarkable Davis Mk3 Lifeboat sextant.  I have no affiliation with the seller or Davis whatsoever other than to have purchased a few items from each of them over the years.

These simple MK3 instruments are perfectly adequate for real navigation. They make a great first sextant due to their simplicity and low cost -- yet you can do some real navigating with them and expect perfectly acceptable results. IMHO they are a better choice than the more expensive plastic sextants that are made to look like "real metal sextants." Those fancier plastic sextants are notorious for never holding their adjustment from one shot to the next in a round of sights which only frustrates beginners. The humble Mk3 doesn't suffer from that shortcoming.
 
If later on you decide to treat yourself to a "fancy metal sextant" you will still keep your MK3 forever because The MK3 is also great for backup; emergency; teaching; and for use on days when the spray is flying and you would prefer not to expose your fancy metal sextant to a salt water dousing.

In fact even if you already own a "fancy metal sextnat" you should consider buying a Mk3 as a backup for those reasons stated above. I did and I am very happy I did so.

On the other hand if you decide that celestial navigation is not for  you, you will be able to sell the MK3 used for about what you paid for it. Or you can just give it to a friend or stash it in the ditch bag. It is a rare "fancy metal sextant" that sells as used for about its original purchase price because people are wary of any unknown history of the instrument and possible hidden defects.

As for myself I started out with an (expensive) fancy metal sextant and turned my nose up at the MK3, although it was suggested to me to start with that model.  Many years later (and a few more "fancy metal sextants" in my collection) I bought a MK3 used.  I can't say enough good things about it. It is one of my favorite sextants. Sure, I'm not going to do lunar distances with it, but I can get position accuracy to within 2 nmi fairly regularly -- and as I said, no worries about eager students dropping it or salt spray ruining it.  In fact just recently I was able to bring down Venus in daylight for practice with the MK3 when my fancier Tamaya failed due to a much smaller field of view.

I love this thing even if it is humble and simple. I will keep mine forever for the reasons stated above, and if it gets somehow destroyed I'd buy a replacement in a minute. I think you would love it too if you would give one a fair try.  In fact the biggest down side to the MK3 is the ribbing you are likely to get about your "inadequate" or "toy" sextant from wanna-be navigators and arm-chair pirates who simply do not know any better.  But after you go out and do a round of sights with it you will be convinced  that they are only displaying their lack of experience.

I have seen it stated in reviews that occasionally the non-adjustable horizon mirror may not be perpendicular to the frame. To check for perpendicularity of the horizon mirror cut about 2mm off the corner of a paper business card at a 45° angle and gently present the card to the mirror as you would a carpenter's square. You need to cut the corner off the business card because there is a tiny plastic ridge at the base of that mirror where its mount meets the frame and  you must create clearance for this ridge. If your horizon mirror is not square you must request a replacement instrument -- it can not be adjusted.  Meanwhile expect to see some of the frame in the right hand side of the horizon mirror even if it is properly perpendicular to the frame. That is normal.

https://www.celestaire.com/product/davis...3-sextant/

A digital sextant. Very interesting.
No sight reduction methods or almanac required.

They claim it can get you a line of position from a single shot of the sun. Or it can give you a position fix with two bodies, or a running fix from two sun sights take some time apart.

What I don't' see is an input for a dead reckoning or assumed position, so how can it work?

A built in ephemeris would give it the geographic position of the observed body and the digital observed altitude would give it a zenith distance, so it would have a circle of position -- but it still needs an azimuth or you could be anywhere on that circle of position.

It must have a flux compass to get an azimuth to the observed body but it doesn't mention it.

Link is below. Skip ahead to about 1:52 to see the digital part described.

I would be curious to hear what others think.

https://www.youtube.com/watch?v=2C9-LMNNzH4

Check out the attached illustration and decide for yourself.

Actually all tracks on the surface of a sphere must be curved in some sense or they would not stay in contact with the surface at all, but a great circle is about as straight a track as you can get while staying on the sphere.  It is all a matter of changing  your perspective.

Once again I don't see great circles taught this way elsewhere.  No wonder people find them confusing.

Simple stuff, I know. The applied math guys are probably rolling thier eyes, but this helped me "get it."

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