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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #11  
Old 02-09-2010
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Quote:
Originally Posted by Flybyknight View Post
Melissa aced the quiz.
What you are looking at is the result of combining the horizon and the equinoctal coordinate systems in order to diagram the celestial triangle on a spherical plane.
This much I got.... what I don't understand is how exactly it works.

Quote:
A discussion of Celestial Coordinates can be found in Dutton's Navigation and Piloting, Chapter 19 "Introduction to Celestial Navigation"
Does it tell you what the diagram means, or does it just discuss celestial coordinates? Lots of books discuss celestial coordinate systems without ever showing such a diagram.
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  #12  
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wind_magic has a spectacular aura about wind_magic has a spectacular aura about wind_magic has a spectacular aura about
I think we could all figure it out if someone who knows for sure would just say what each of the points with labels on them is, and the lines. Even with the points and lines in the quiz answered it hasn't been enough for me to figure out what I am looking at.
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  #13  
Old 02-09-2010
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Precisely... I feel like this could be a very useful diagram if only I could hear the line of reasoning that goes into constructing and labeling it.
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AdamLein, let's try to figure it out then.

I agree that M must be the thing being sighted, because those two unlabeled lines running parallel to AE and BF look like they are measuring something, probably longitude and latitude offsets (angles or actual distance) from the lines they run parallel to.

I agree too that C looks like the zenith.

DH looks like a declination of some kind from AE and BF, but I don't really get that, but I wonder if the angle made by DH to AE and BF is significant at point X (?).

Hard to guess.
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Old 02-09-2010
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Get the Freak out of here.. I got it right...Dang.. Running out the door now at full sprinter speed to buy a lotto ticket.. Be back in a flash!
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  #16  
Old 02-09-2010
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Quote:
Originally Posted by AdamLein View Post
If the equator is BF as you suggested, how can the north pole be B or F?
I change my mind in my next post and said the North pole is BF and equator is AE. There are three lines that intersect X to show the center. The three lines are
1.North pole is BF with F the north pole due to the way the arc is drawn.
2. AE the equator and horizon. There should be another line drawn I believe to show the horizon if not on the equator.
3. The sighting arc from horizon to horizon. Why I also thought we were on the equator. Should be a horizon line. Also the way the arc is drawn and how a star travels across the sky from east to west. If this sighting was the southern cross for which I suspect it is ( My big assumption) is about the right position in the sky on the equator. I get to see this every week when I fly down to South America.
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  #17  
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Navigational Coordinates

I hope this turns out to be legible, if not, I would be happy to
retype the essentials and email, if interested.
Quoting my text: "It is vital to have a thorough understanding of the Navigational Coordinates and other terms referenced to the celestial sphere if the motion of celestial bodies is to be understood"
Best to All.
Dick


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Cannot read the chart. email it to me if you can. Thanks
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  #19  
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Need to Copy And Snail Mail

Quote:
Originally Posted by Melrna View Post
Cannot read the chart. email it to me if you can. Thanks
Hello all,
well I tried to determine legibility by emailing the sheet to myself but it did not work. If you would like a copy, pm me a snail mail address.

Dick
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Old 02-10-2010
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Okay so I just spent the last hour trying to reconstruct this crazy diagram and determining that all my intuitions are wrong. So I'm starting from scratch, and using the following problem solving strategy: wishful thinking. In other words, I'd like this diagram to be navigationally useful, so it has to give me a way of computing altitude and azimuth, given declination and local hour angle.

Altitude is the distance along the vertical circle from the horizon to the body being sighted. Azimuth is the distance from the north point on the horizon, to the point where the vertical circle touches the horizon.

Therefore I'd like it if most of the "work" of making the diagram involves producing the vertical circle. This should be represented by a figure on the diagram that intersects the horizon and also intersects another line which will represent the body's meridian. It seems like that arc should be the vertical circle; once I have it I know where the body is. The distance from X to the chord intersecting DX yields the altitude, and the distance from X to the arc along BX should yield the azimuth (possibly after doing some trig like taking the arcsine).

There are three inputs here that need to be explicitly included in the diagram's construction: my latitude, the body's declination, and the body's local hour angle.

The problem I'm running into is that there are three variables, but I can only figure out how to include two in the diagram: latitude and declination.

I've constructed this diagram a dozen times and I keep running into a wall in terms of how to include local hour angle. I'm basically giving up until I can get a copy of that book.
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