Senior Member

LinkBack  Thread Tools 
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.
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.
Quote:
A discussion of Celestial Coordinates can be found in Dutton's Navigation and Piloting, Chapter 19 "Introduction to Celestial Navigation"
s/v Laelia  1978 Pearson 365 ketch
s/v Essorant  1972 Catalina 27
Sponsored Links  
Advertisement


Senior Member
Join Date: Jun 2006
Posts: 5,006
Thanks: 5
Thanked 18 Times in 18 Posts
Rep Power: 12
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.
What are you pretending not to know ?
Please support my
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Senior Member
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.
s/v Laelia  1978 Pearson 365 ketch
s/v Essorant  1972 Catalina 27
Senior Member
Join Date: Jun 2006
Posts: 5,006
Thanks: 5
Thanked 18 Times in 18 Posts
Rep Power: 12
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.
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.
What are you pretending not to know ?
Please support my
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Crazy Woman Boat Driver
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!
Melissa Renee
Moondance
Catalina 445, Hull #90
Crazy Woman Boat Driver
Quote:
Originally Posted by AdamLein
View Post
If the equator is BF as you suggested, how can the north pole be B or F?
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.
Melissa Renee
Moondance
Catalina 445, Hull #90
Senior Member
Join Date: Nov 2005
Location: Milton, DE
Posts: 592
Thanks: 2
Thanked 7 Times in 7 Posts
Rep Power: 11
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
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
Crazy Woman Boat Driver
Cannot read the chart. email it to me if you can. Thanks
Melissa Renee
Moondance
Catalina 445, Hull #90
Senior Member
Join Date: Nov 2005
Location: Milton, DE
Posts: 592
Thanks: 2
Thanked 7 Times in 7 Posts
Rep Power: 11
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
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
Senior Member
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.
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.
s/v Laelia  1978 Pearson 365 ketch
s/v Essorant  1972 Catalina 27

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)  
Thread Tools  
Show Printable Version Show Printable Version
Email this Page Email this Page


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Windward performance  deseely  General Discussion (sailing related)  21  04012012 03:42 PM 
Fin Keel or Shoal Keel  acmecoyote  General Discussion (sailing related)  11  05062011 05:39 PM 
What can you tell from the numbers?  brazilnut  Boat Review and Purchase Forum  10  07012009 05:09 PM 
Best Hull type?  Vastbinder  General Discussion (sailing related)  24  10212006 01:14 AM 
Sailing to deeper waters (The Coast Star)  NewsReader  News Feeds  0  08272006 04:15 PM 
Posting Rules  