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Old 12-01-2015, 14:02   #1
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Celestial Nav. Problems for Fun

I enjoying doing celestial navigation problems, especially now when it's winter and minus 25 outside like yesterday, So i thought I would start a thread just for Celestial Nav. problems.

If there is enough interest, we will keep it going. Please feel free to submit your own celestial navigation problems. I find that creating problems forces you to approach celestial navigation a different way since, I am not actually taking sights and things need to fit together or else you end up with intercepts of 400 to 500nm'S.

So here is my problem - I will submit my answer in a few days after those interested have had an opportunity to figure it out on their own.

Lat. at Noon Question

Sun LL
Date: July 17th, 2014
Z +8
WE (watch error) Fast 1m27s
Index (off) 2m
Anticipated DR at noon: DR 49 degrees 05N
128 degrees 15W

A) What time do you anticipate LAN (Local Apparent Noon)?


b) Based on your series of sightings around noon, you determine that LAN occurred at: 20h 44m 29s UTC

Using your DR Lat and the following information, determine your Lat.

Sun LL
UTC 20h 44m 29s
Hs 47 degrees 09m
Index off 2m
Height of Sight 12.5 ft

C) What is your estimated Long.?

D) What was your watch time of noon?

Good Luck, Les
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Old 12-01-2015, 15:53   #2
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Re: Celestial Nav. Problems for Fun

Answer to A- LAN on 7/17/2014 was on UTC 20:39:11.2


Comment- watch error has nothing to do with calculating LAN in this situation as you're basing the time upon your estimated position of W 128d 15 min using GHA of that EP (estimated position). But...to take into account your watch error....


LAN would be (looking at your watch) 20:37:44.2


Answer to B- Latitude at UTC 20:44:29 was N 63d 43 min 20 sec


Solution= 90d - Ho (47d 22min 34sec) + Sun Declination (N21d 05.9min)


Answer to C- Estimated Longitude at UTC 20:44:29 was W 129d 34.6 min


Watch error wasn't taken into consideration for that answer. To take into account a watch error of +1 min 27sec the.....Answer to C- Estimated Longitude at UTC 20:43:02 was W 129d 12.8min


Answer to D- Watch time at LAN was 20:43:02



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Old 12-01-2015, 16:59   #3
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Re: Celestial Nav. Problems for Fun

I probably should have said Local
Time not watch time?

PDA1 your Ho is considerably different than mine - not sure you included the "main" correction for the sun.

I will post my answer after a few more responses to the thread.


Sent from my iPhone using Cruisers Sailing Forum
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Old 12-01-2015, 17:42   #4
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Re: Celestial Nav. Problems for Fun

Local time will only confuse matters. Stick to UTC. Also, my assumption is that my watch is always correct to within 1 second of time using WWV. If you know that your watch is off by a certain amount then you really do know what time it should be and your watch should be set to the exact time. It makes life a lot easier.

I use an acronym to remember the corrections necessary to Hs- it's D.R.I.P.S.

Here's how I arrived at Ho;

Hs- 47d 09min

Dip- -3.4min

Refraction- 0d .887 min (based on .99/Tan(Ha)

Index Error- +2min (so it's subtracted from Hs)

Parallax- + .1min (about that much. It's insignificant)

Semi-Diameter- + 0d 15.76min (July 18)

Ho= 47d 22min 34.38sec (rounded up- 47d 22.6min)

If you want to be sloppy about it just use the Altitude Correction Tables for a simple figure to add to Hs of 0d 15.1min. Added to Hs that would give you Ho of 47d 24.1min which is really an insignificant difference to the "proper" measurement.

This is fun. 'Glad you started this thread.
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Old 12-01-2015, 18:22   #5
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Re: Celestial Nav. Problems for Fun

Quote:
Originally Posted by PDA1 View Post

Semi-Diameter- + 0d 15.76min (July 18)

I don't know how the "July 18" appears to you but my side of the screen shows some stupid orange thing with sun glasses. 'No idea how it got there. Computers!
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Old 12-01-2015, 18:25   #6
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Celestial Nav. Problems for Fun

I was trying to throw in that it would be daylight savings time so to subtract 1 hour and fact that your time piece is fast

I don't see the stupid orange thing on yours but I see it on my text when I send a reply - please go away orange thing
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Old 12-01-2015, 18:35   #7
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Re: Celestial Nav. Problems for Fun

Quote:
Originally Posted by GoSailing View Post
I was trying to throw in that it would be daylight savings time so to subtract 1 hour and fact that your time piece is fast
Understood. In celnav all my clocks (all 2 of them) are set to UTC by way of WWV and I don't take local time into consideration.
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Old 13-01-2015, 18:40   #8
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Re: Celestial Nav. Problems for Fun

So I answered my questions using the nautical almanac, arc to time table, declination corrected, 'main' correction for the sun etc.

A) 20h 40m 29s (did not correct for watch error since I was using UTC time)
B) Lat. 63d 44.2'
C) Long. 129d 37.15'
D) 20h 45m 56s

All that said, I am within shouting distance of PAD1

Les
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Old 13-01-2015, 19:18   #9
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Re: Celestial Nav. Problems for Fun

Pretty close!

Good enough I'd say.

That was fun!

Thanks.
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Old 13-01-2015, 22:35   #10
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Re: Celestial Nav. Problems for Fun

It's not winter here! Top of New Zealand, and it's about 30 degrees C! Shorts, T shirt, and sun lotion. Sorry guys, you probably don't need to hear that.

Anyway, here's a challenge for you, if it hasn't already been done. Write software to find the longest straight route possible to sail on earth. It would probably start at the top of the Pacific or the Atlantic, and cross diagonally, passing close by Antarctica (in our Southern Summer) and then back up the Atlantic.

Then go sail it! You'd get in the Guinness book of records!
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Old 14-01-2015, 06:39   #11
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Re: Celestial Nav. Problems for Fun

Great weather you have!
Warmth? Yes, I remember that...a long time ago.

I assume you mean a Great Circle route. The following is an edited quote found someplace on the web-

"The longest open sea great circle route that can be found on Earth runs from Pakistan to far eastern Russia- you'll sail out of the Indian Ocean, under Cape Horn, and then all the way up the Pacific to Kamchatka, and...you will never bump into any significant land".

Here's the formula-

(For abreviation "DLo" stands for "Difference in Longitude between Beginning and End")

Initial Bearing-

tan-1(sin(DLo) / (cos(Departure Latitude) x tan(Destination Latitude) - (sin(Departure Latitude) x cos(DLo))

If Azimuth calculated is negative add 180d to it.
If DLo is negative add 180 to it.

BE VERY CAREFUL WHEN USING THAT FORMULA! Keep in mind which quadrant you'll initially be sailing or you'll end up going on a really wrong angle. While it does solve the initial bearing problem it's a very tricky formula.


Distance-

90-sin-1((sin(Destination Latitude) x sin(Departure Latitude) + cos(Destination Latitude) x cos(Departure Latitude) x cos(DLo))

Multiply the answer by 60 to get nautical miles

You can find these formulas in Bowditch Chapter 22 and Chapter 24 here;

http://msi.nga.mil/NGAPortal/MSI.por...2&pubCode=0002

OpenCPN already has a great circle plugin so you can just graphically pick departure and destination points and it'll calculate the rest.
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Old 15-01-2015, 07:52   #12
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Re: Celestial Nav. Problems for Fun

How about a really simple problem in 2 parts?

Your location- S15d 21min W062 53min

1- What is the Sun's GHA on January 15, 2015 at UTC 04:36:07

2- Can you take a Sun sight at your location and at that time?

You can get 2015 The Nautical Almanac here-

http://TheNauticalAlmanac.com
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Old 15-01-2015, 12:03   #13
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Re: Celestial Nav. Problems for Fun

[QUOTE=PDA1;1725413]How about a really simple problem in 2 parts?

Your location- S15d 21min W062 53min

1- What is the Sun's GHA on January 15, 2015 at UTC 04:36:07

2- Can you take a Sun sight at your location and at that time?


Sun's GHA 246d 51.4
Under a low pressure system, won' be able to see the Sun today.

So I thought I would figure out the Hc.
LHA 182
ALat 15
Dec. Cor. 21d 08.4'

Using HO249, "same" page for 15 degrees, I could not find a LHA of 182?

So I thought I would use the calculator method and this is what I came up with for the Hc.

Hc 53d 46'
Zn=75d
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Old 15-01-2015, 12:12   #14
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Re: Celestial Nav. Problems for Fun

Here's a question back:

Sun UL
July 4, 2014
DR S 49d 17'
E 128 d 46.1'
UTC 4h 25m 17s

Hs 17d 37.7
Index On 3 min
Ht. of Eye 13ft

Whats the Ho, Hc, Intercept and Zn
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Old 15-01-2015, 13:01   #15
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Re: Celestial Nav. Problems for Fun

[QUOTE=GoSailing;1725607]
Quote:
Originally Posted by PDA1 View Post
How about a really simple problem in 2 parts?

Your location- S15d 21min W062 53min

1- What is the Sun's GHA on January 15, 2015 at UTC 04:36:07

2- Can you take a Sun sight at your location and at that time?


Sun's GHA 246d 51.4
Under a low pressure system, won' be able to see the Sun today.

So I thought I would figure out the Hc.
LHA 182
ALat 15
Dec. Cor. 21d 08.4'

Using HO249, "same" page for 15 degrees, I could not find a LHA of 182?

So I thought I would use the calculator method and this is what I came up with for the Hc.

Hc 53d 46'
Zn=75d
GHA is 246d 42.4'

LHA is 204

Hc is -53d 45.5'

Zn is 173d

No, you can't take a Sun sight at that location and time. It's dark.
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