Celestial Nav. Problems for Fun

[PDA1]

Originally Posted by GoSailing

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

Ho= 17d 15.3' (about)
Hc= 17d 02.4' (about)

Intercept= 12.8 nm Towards
Zn= 346.5d

[PDA1]

[QUOTE=PDA1;1725652]

Originally Posted by GoSailing

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.

Whoops....make that LHA 184d

Hc= -53d 36.0min

....and Zn= 149d

[DefinitelyMe]

Originally Posted by PDA1

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-

The Nautical Almanac

It says 'error 404 not found' when i try to download the almanac. Is it just me that it isn't working for?

[Gos2015]

That explains why I can't see the sun at night. I thought there was something wrong with my sextant - tried it with all filters off and still couldn't see the Sun


Sent from my iPhone using Cruisers Sailing Forum

[PDA1]

Originally Posted by GoSailing

That explains why I can't see the sun at night. I thought there was something wrong with my sextant - tried it with all filters off and still couldn't see the Sun


Sent from my iPhone using Cruisers Sailing Forum

Try the Infrared band.

[PDA1]

Originally Posted by DefinitelyMe

It says 'error 404 not found' when i try to download the almanac. Is it just me that it isn't working for?

Works ok for me.

Try clearing your cache/history.

Which file are you trying to download?

[PDA1]

Here's a more thought out answer to the problem you posed. Working in Southern & Eastern Latitudes was something I've not done before.

Date- 7/4/2014
UTC- 04:25:17
Hs- 17d 37.7
Limb- Upper

Ho= 17d 15.8'

GHA= 245d 13.8'

Ap Lat= S 49d
Ap Long= E 128d 13.8'

LHA= 13d (I had forget to ADD Eastern Ap Longitudes to GHA)

Hc= 17d 11'

Zn= 347d

Intercept= 5 nm (approx).

[PDA1]

I have an idea.

For curiosity I'll take a picture of the plotted Intercept and LOP that was the result of the problem you presented and let's see how close it comes to the DR Latitude and DR Longitude. My answer to your problem was derived using the Ap Latitude and Ap Longitude.

[PDA1]

Here are pictures of the plotted LoPs based on 2 different LHA figures;

13d
14d

Typically, I do sight reductions using HO-249 and an Ap Lat. and Ap. Long. and not the DR figures. The Ap. Longitude figure is based on GHA minutes of arc and the whole Ap. Longitude figure.

Mathwise the LHA of 14d is based on a figure of around 13d 59min LHA so it really is much closer to 14d than it is to 13d....IF you were adding the whole DR Long. to the whole GHA (adding GHA to Ap. Long. is Eastern Longitudes).

Also, there's a picture of the official "on-the-hard" navigation station. Notice the T-plotter I made.

[Gos2015]

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

So this is what I got to my own question using A. Lat., A. Long., Ho 249 for 2014

Hc 17d 11'
Ho 17d 12.4'
LHA 14d
Z= 167d
ZN= 347d
a = 1.4NM

I am having trouble duplicating (or even coming near) my Hc using the calculator.

Re: photos - pretty darn close to DR Lat & Lo

Good idea for T ruler, I have been using a right angle triangle.

I will try some more with the calculator and if I can't figure it out, I will post my attempts for assistance.

[PDA1]

Originally Posted by GoSailing

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

So this is what I got to my own question using A. Lat., A. Long., Ho 249 for 2014

Hc 17d 11'
Ho 17d 12.4'
LHA 14d
Z= 167d
ZN= 193d
a = 1.4NM

I am having trouble duplicating (or even coming near) my Hc using the calculator.

Re: photos - pretty darn close to DR Lat & Lo

Good idea for T ruler, I have been using a right angle triangle.

I will try some more with the calculator and if I can't figure it out, I will post my attempts for assistance.

I got your Hc of 17d 11.6min

How I entered in my calculator;

sin-1(sin(-49) x sin(22d 52.9min) + cos(-49d) x cos(22d 52.9min) x cos(13d)

You can use either negative Declination OR negative Ap. Latitude. But, one of the figures must be negative as your Ap. Lat. and Declination are of Contrary Name.

Using an LHA of 14d will give an Hc of 17d 2.4min.

Note also that the "x" (times sign) isn't necessary when using my Casio calculator.

Also, I should "round-up" the figure of Declination to 22d 53min. 22d 52.9min might as well be 22d 53min for our purposes.

I got the "T-Plotter" idea from Peter Hakel's work who has the Celestial-Navigation Spreadsheets on the web. The Longitude scale is set for my Latitude and I printed it out on my computer, then, taped it onto the "T". Pretty simple. Sure beats using dividers.

[Gos2015]

Figured out the calculator:

Hc 17d
Z 166
Zn 346d

[PDA1]

Originally Posted by GoSailing

Figured out the calculator:

Hc 17d
Z 166
Zn 346d

Nice. So we're back to within shouting distance.

[Gos2015]

Question for the weekend:

Jupiter
Sept 23, 2014
DR Lat 48d 12' N Lo 143d 24' E
UTC 15h 13m 21s
Hs 20d 18.9'
Index Off 2m 20s
Ht. of Eye 4M
Crew: unruly

[PDA1]

Here's the Jupiter reduction;

Note- some rounding up, or down, of numbers was done as tenths of a minute of arc aren't significant.

DR Latitude= N 48d 12min
DR Longitude= E 143d 24min

Date- 9/23/2014
UTC- 15:13:21
Hs= 20d 18.9min
IE= Off 0d 2min 20"
He= 4 meters (I set it to 12 feet)

Hs- 20d 18.9min
IE- +0d 2min
Dip- 0d 3.6min
Ha= 20d 17.3min

Altitude correction= -2.6min

Ho= 20d 14.7min (call it 20d 15min)

GHA= 93d 29.4min
"v"/"v correction"= 2min/0.5min
GHA= 93d 30min

Declination= N 16d 56.2min
"d"/"d correction"= 0min.1/0.0min
Declination= N16d 56.2

Ap Latitude= N 48d
Ap Longitude= E 143d 30min
LHA= 236d

Hc= -8d 7.9min
Zn= 53d

(Zn isn't absolutely certain as Hc is negative and therefore Jupiter isn't visible)

Hc using an LHA of 236d 53.9min based on the DR Longitude= -8d 14min

Crew: put in irons