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Thread: Hello
Post: RE: Hello
| Mike,
The purpose of an assumed position (AP) has nothing to do with the underlying math.The purpose is to make the tables compact enough to carry aboard. The AP is simply a contrived "trial positio... |
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PeterB |
The Sight Reduction process
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11 |
5,345 |
11-23-2023, 09:39 PM |
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Thread: Electronic Charts: New Book
Post: Electronic Charts: New Book
| David Burch of Starpath School of Navigation has just released a new book "ENC Essentials" dealing with the transition from paper charts to electronic navigation charts.
It is available from Amazon a... |
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PeterB |
Equipment- Wanted or for Sale
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0 |
557 |
10-15-2023, 01:37 PM |
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Thread: assumed longitude
Post: RE: assumed longitude
| Rumata,
Conceptually you are not wrong to think that the order in which you do your sums should make any difference to the outcome.
If you used a calculator or computer program to do the sight reduc... |
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PeterB |
General Topics Here
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2 |
1,468 |
10-07-2023, 07:41 PM |
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Thread: What Is Your Favorite Watch?
Post: RE: What Is Your Favorite Watch?
| Quartz watches are amazing- they put an end to mechanical watch dominance. But....mechanical watches are beautiful- especially considering how they are made (I refer to the expensive ones).
I agree... |
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PeterB |
Equipment- Wanted or for Sale
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3 |
2,346 |
08-26-2023, 05:46 PM |
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Thread: What Is Your Favorite Watch?
Post: What Is Your Favorite Watch?
| I used to use a small-ish TIMEX IronMan watch that had a metal band. It was easy to read and served well but the band had a tendency to tear out of the lugs on the watch case, which was resin, after ... |
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PeterB |
Equipment- Wanted or for Sale
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3 |
2,346 |
08-21-2023, 02:48 PM |
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Thread: Help With an Exam Question
Post: Help With an Exam Question
| Today is May 5th 2023 so this seems like a good time to post the following
A long while back on an obscure forum that I can't seem to find again I found this response to a poster seeking help on a ... |
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PeterB |
Humor & Laughter
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1 |
1,436 |
05-05-2023, 02:34 PM |
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Thread: USCG Crazy Exam question: Sidereal vs Tropical Year
Post: RE: USCG Crazy Exam question: Sidereal vs Tropical...
| Here are two other links you might like. One is to another practice exam, the other is to the "Training Almanac for 1981" that you need to use for all of the practice exam celestail problems and which... |
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PeterB |
General Topics Here
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3 |
2,485 |
05-04-2023, 08:48 PM |
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Thread: USCG Crazy Exam question: Sidereal vs Tropical Year
Post: USCG Crazy Exam question: Sidereal vs Tropical Yea...
| USCG Exam Question Sidereal vs Solar (Tropical) Year
I was poking about and came across a USCG practice exam here:
https://www.dco.uscg.mil/Portals/9/NMC/pdfs/examinations/q154_nav_problems-ocea... |
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PeterB |
General Topics Here
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3 |
2,485 |
05-02-2023, 05:02 PM |
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Thread: How to get LHA and Ap longitude in Eastern longitudes
Post: RE: How to get LHA and Ap longitude in Eastern lon...
| Fred_B,
You most certainly can wind up with a DR and resulting AP that are a long way from where you actually were. However the resulting LOP is not entirely "bad" although it is not as "good" as ... |
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PeterB |
General Topics Here
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15 |
7,698 |
04-28-2023, 10:06 PM |
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Thread: How to get LHA and Ap longitude in Eastern longitudes
Post: RE: How to get LHA and Ap longitude in Eastern lon...
| Paul,
An example of finding the AP longitude in western longitudes including adjusting the AP lon to be within 30.0' of the DR lon.
A sight of the sun's lower limb was taken on July 15, 2022 at ... |
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PeterB |
General Topics Here
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15 |
7,698 |
04-22-2023, 04:49 PM |
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Thread: How to get LHA and Ap longitude in Eastern longitudes
Post: RE: How to get LHA and Ap longitude in Eastern lon...
| Paul,
The short answer is "No, the process is not the same in western longitudes." The good news is that it is some what easier to do and less confusing.
The Greenwich Hour Angle (GHA) of the body... |
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PeterB |
General Topics Here
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15 |
7,698 |
04-19-2023, 09:32 PM |
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Thread: How to get LHA and Ap longitude in Eastern longitudes
Post: RE: How to get LHA and Ap longitude in Eastern lon...
| HI, Ed,
It sounds as if you have got this squared away.
I am pleased that you actually did the sight reduction and plot from both AP's to see that the resulting LOP's are both valid. It is one... |
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PeterB |
General Topics Here
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15 |
7,698 |
04-08-2023, 03:28 PM |
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Thread: How to get LHA and Ap longitude in Eastern longitudes
Post: RE: How to get LHA and Ap longitude in Eastern lon...
| Hello Ed,
The only reason you need to be less than 30' difference in longitude from your DR is to please the examiner and to get the same answer as he did for Z and Hc.
If you pick the "wrong... |
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PeterB |
General Topics Here
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15 |
7,698 |
04-04-2023, 05:48 AM |
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Thread: How to get LHA and Ap longitude in Eastern longitudes
Post: RE: How to get LHA and Ap longitude in Eastern lon...
| I got different results from my page xi Pub 249
An example of when the “short cut” method of finding your LHA in Eastern longitudes gets it wrong and why you should not rely on it.
This is taken... |
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PeterB |
General Topics Here
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15 |
7,698 |
04-02-2023, 08:27 PM |
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Thread: why Astron uses a "decide for yourself" AP longitude
Post: RE: why Astron uses a "decide for yourself" AP lon...
| I'm glad that it helped.
Peter |
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PeterB |
General Topics Here
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2 |
1,672 |
03-31-2023, 01:21 AM |
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Thread: why Astron uses a "decide for yourself" AP longitude
Post: why Astron uses a "decide for yourself" AP longitu...
| Carlos Pindle had mentioned he did not understand why the Astron app allows you to use a "decide for yourself" latitude and longitude for an assumed position.
I will try to shed some light on that ... |
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PeterB |
General Topics Here
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2 |
1,672 |
03-30-2023, 08:51 PM |
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Thread: A Source of Confusion in Selecting an Assumed Position
Post: RE: A Source of Confusion in Selecting an Assumed ...
| Carlos
The confusion is the mislabeling of Assumed Position in the app.
That should have been labeled either " Dead Reckoning Position" or "Estimated Position."
Since it is an electronic calc... |
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PeterB |
General Topics Here
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8 |
4,979 |
03-30-2023, 12:20 PM |
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Thread: A Source of Confusion in Selecting an Assumed Position
Post: RE: A Source of Confusion in Selecting an Assumed ...
| Paul,
I am glad that my post has been helpful.
I have never used the Doniol method. Perhaps I will give it a try one of these days.
Peter |
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PeterB |
General Topics Here
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8 |
4,979 |
03-28-2023, 09:40 PM |
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Thread: A Source of Confusion in Selecting an Assumed Position
Post: RE: A Source of Confusion in Selecting an Assumed ...
| Carlos
I imagine some people still use Ageton's (H.O. 211) because it is readily available, often as a free download. In addition there are a number of variations of it available, also often for free... |
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PeterB |
General Topics Here
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8 |
4,979 |
03-28-2023, 03:31 PM |
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Thread: A Source of Confusion in Selecting an Assumed Position
Post: RE: A Source of Confusion in Selecting an Assumed ...
| Paul,
First thank you for your question. I know this is initially a point of confusion for many and I worried that no questions meant I did not explain it very well! Full disclosure: It confused the... |
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PeterB |
General Topics Here
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8 |
4,979 |
03-27-2023, 05:13 PM |
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Thread: A Source of Confusion in Selecting an Assumed Position
Post: A Source of Confusion in Selecting an Assumed Posi...
| My apologies if this post is a little long, but if selecting an AP in the Eastern longitudes has you confused this might get to the heart of the reason why. I try to be complete in my discourse becaus... |
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PeterB |
General Topics Here
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8 |
4,979 |
03-26-2023, 04:24 PM |
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Thread: compass rose revised
Post: RE: compass rose revised
| Pabrides
In surveying and to a certain extent in advanced navigation bearings are often given with a reference direction, a number of degrees, and a direction to sweep.
For example: N 30° W spok... |
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PeterB |
General Topics Here
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2 |
2,830 |
03-14-2023, 09:35 PM |
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Thread: Hello
Post: RE: Hello
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CarlosPindle Wrote: (03-10-2023, 02:47 PM)
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Peter,
Will you please explain the meridian t angle stuff. I've read about it but it has always been too difficult to understand. Why not just use LHA... |
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PeterB |
The Sight Reduction process
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11 |
5,345 |
03-11-2023, 02:13 PM |
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Thread: Hello
Post: RE: Hello
| I use the following: here " t " is the meridian angle either east or west
Sin(Hc) = Sin(L)Sin(d) + Cos(L)Cos(d)Cos(t)
Tan(Z) = Sin(t) / [Sin(L)Cos(t) – Cos(L)Tan(d)]
When I do sight redcutio... |
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PeterB |
The Sight Reduction process
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11 |
5,345 |
03-09-2023, 06:35 PM |
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Thread: UPS set to 60 minutes?
Post: RE: UPS set to 60 minutes?
| You are absolutely correct that you may set up the plotting sheet using a scale of 60 arc-seconds on the central longitude line instead of the usual 60 arc-minutes. You would find the correct placeme... |
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PeterB |
The Sight Reduction process
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1 |
1,366 |
03-09-2023, 06:19 PM |
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Thread: Sextant mirrors re-silvering
Post: RE: Sextant mirrors re-silvering
| There are several optical coating services for amateur telescope makers who should be able to strip and re "silver" your mirrors. Actually they don't call it"silvering" anymore since the use high per... |
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PeterB |
General Topics Here
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2 |
2,274 |
02-03-2023, 09:49 PM |
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Thread: LHA in Eastern longitudes?
Post: RE: LHA in Eastern longitudes?
| East Longitude Hour Angles Reply
To find a Calculated Altitude (Hc) and True Azimuth (Zn) to compare to our observed altitude (Ho) we need to solve the navigation triangle.
We also need the exact sp... |
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PeterB |
General Topics Here
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5 |
4,170 |
12-31-2022, 07:39 PM |
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Thread: Sale on Davis Mk3 "Lifeboat" sextant
Post: Sale on Davis Mk3 "Lifeboat" sextant
| 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 wit... |
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PeterB |
Equipment- Wanted or for Sale
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0 |
1,204 |
04-30-2022, 03:57 PM |
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Thread: Digital Sextant
Post: Digital 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 w... |
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PeterB |
General Topics Here
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0 |
1,247 |
04-26-2022, 06:37 PM |
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Thread: Are Great Circle Tracks Curved ?
Post: Are Great Circle Tracks Curved ?
| 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, b... |
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PeterB |
General Topics Here
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0 |
1,074 |
04-22-2022, 07:28 PM |
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Thread: Why Great Circles Are Great
Post: Why Great Circles Are Great
| I have many books on celestial navigation and none of them explain the simple elegance of great circles as used in c-nav. That is a shame because they are easy to understand without any fancy mathemat... |
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PeterB |
General Topics Here
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0 |
4,718 |
04-14-2022, 09:03 PM |
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Thread: What Day Is It In Greenwich
Post: What Day Is It In Greenwich
| In a much earlier post on this forum titled “A Celestial Navigation Problem I Can't Solve”
There was discussion regarding the determination of the correct Greenwich day and date. The confusion ari... |
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PeterB |
General Topics Here
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0 |
1,198 |
04-08-2022, 03:37 PM |
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Thread: About (Daylight) Time
Post: About (Daylight) Time
| The US senate has recently passed an article to make Daylight Savings Time (summer time when the clocks are set one hour ahead) permanent. This isn't the first time the USA has experimented with this ... |
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PeterB |
General Topics Here
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0 |
1,118 |
04-03-2022, 05:08 PM |
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Thread: Sextant - what are these bits for?
Post: RE: Sextant - what are these bits for?
| NeilS
It sounds like you did well with your old Tamaya.
Don't worry about cleaning up the scales on the arc with a bit of Brasso. After all if you can't read them the sextant is pretty much usel... |
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PeterB |
General Topics Here
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6 |
5,632 |
03-23-2022, 02:26 PM |
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Thread: Venus in Daylight My First Time
Post: Venus in Daylight My First Time
| March 21 2022
Today is the unofficial first day of spring and it is the first day in many when my local skies have been clear.
Venus is visible during the daylight hours right now and will be for ... |
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PeterB |
General Topics Here
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2 |
2,253 |
03-21-2022, 05:21 PM |
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Thread: Sight Calc App for Sight Reduction
Post: Sight Calc App for Sight Reduction
| There is a free app available for smart phones called
"Sight Calc"
It is very straight forward and will provide you an azimuth, a true azimuth, and a calculated altitude for any input of Latitud... |
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PeterB |
The Sight Reduction process
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0 |
1,454 |
03-18-2022, 08:10 PM |
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Thread: Sextant - what are these bits for?
Post: RE: Sextant - what are these bits for?
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neil_s Wrote: (01-30-2022, 08:32 PM)
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Hi to all - I am new on the site and a relatively new self taught celestial navigator - I've been hooked for about three years, now. There are a couple of thin... |
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PeterB |
General Topics Here
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6 |
5,632 |
03-18-2022, 07:53 PM |
