Hi Shipmates,
Here is a complicated issue - or maybe its a non-issue that Ive made complicated:
When using a calculator to find Hc, does one enter the same whole numbers that are used when looking up Hc/d/Z in 249/229? Or does one enter into the formula an APLAT, DEC, and LHA with decimal values (degrees:minutes:seconds) included?
I mean, as I try to think logically about this, if you can create your own assumed position (AP) wherever you like, then you can place the AP as close to the DR as you like, and as close to the body's Zn as possible. Then the LOP would consistently line up very near the actual HO position reducing error a great deal (as long as the actual position is relatively close to DR).
The same question applies to finding Z...
Tell me what you think!
Joe
Joe,
Avast there! It's pretty simple. Yes, you can use the whole degree figures for Ap latitude (Assumed position latitude) Declination and LHA. But, to make it more accurate you should use the declination figure found in The Nautical Almanac which includes the degrees and minutes of the declination. Of course you could use the Ap latitude degrees and minutes and Ap longitude degrees and minutes (in the "Cos(LHA)" portion of the formula (cos(GHA - Ap longitude) also if you wanted. The same applies to finding azimuth with the Z formula.
Carlos
(08-31-2018, 09:31 AM)CarlosPindle Wrote: [ -> ]Joe,
Avast there! It's pretty simple. Yes, you can use the whole degree figures for Ap latitude (Assumed position latitude) Declination and LHA. But, to make it more accurate you should use the declination figure found in The Nautical Almanac which includes the degrees and minutes of the declination. Of course you could use the Ap latitude degrees and minutes and Ap longitude degrees and minutes (in the "Cos(LHA)" portion of the formula (cos(GHA - Ap longitude) also if you wanted. The same applies to finding azimuth with the Z formula.
Carlos
Thanks, Carlos, that's the answer I anticipated. Ive been working with my new HP-35s calculator which has a weird hh:mm:ss to hh.decimal conversion function (there are no corresponding colons or other marks to separate hours from minutes or seconds. I can't enter dd:mm.dec directly so I use the HMS function to enter dd.mmss. However I dont know how or when the calculator discovers that Im entering dd.ddd... or dd.mmss values to which are applied trig functions in the HC or Z formula.
Ex:
Say declination is 08:36.7
I can't enter 8.36.7 directly - then the calculator thinks Im entering a fraction 8 36/7
I must enter 8.3642 which is interpreted as 8 degrees:36 min:42 seconds (.7x60)
I multiply the 7x6 in my head
Then I press the trig function
Sin 8.3642 = .1455
However
Sin 8.6117 = .1497 8.6117 is the decimal equivalent of 8:36:42 (DMS)
It doesnt work well. Which is right? The .1497 I think.
I must remember to enter DEC as dd.ddd... if I am to enter other than whole numbers to find Hc.
Adding time values or degree values, as when averaging observations, is not difficult. Im still learning about this calculator and RPN (Reverse Polish Notation). Its been a challenge - but that's why I like it. Your post has given me the knowledge to explore this notation issue.
One more thing.... If you use DEC with the fractional decimal, do you use it before or after the d correction?
joe