NavList:

Would you please be able to give me a sample problem and work through the
answer so that I can repeat the steps and know I'm getting to the correct
answer. I appreciate your help.
Guy

----- Original Message -----
From: "Bill Burchell" <wrburchell@earthlink.net>
To: <NavList@fer3.com>
Sent: Wednesday, May 03, 2006 10:14 PM
Subject: [NavList 113] Re: Please help me with the math Re: learning sight
reduction


>
> Guy wrote:
>
>> OK so here is the formula I have sin
>> (Hc)=sin(dec)sin(lat)+cos(dec)cos(lat)cos(dlo)
>> question 1 is dlo the same as LHA? if not what is dlo?
>
> Not certain.  I think of dlo as the smallest angle (absolute value) that
> expresses the difference between two longitudes.
>
> LHA is the angle measured WESTWARD from the observer's position to the
> body
> (GHA).  If the body is west of the observed, that will be the same as dlo.
> If the body is east of the observer, you will have to go all the way
> around
> to get to the observer.
>
> Example:
>
> AP lon 80d W
> Body GHA (lon) 60d W
> dlo = 60 - 80 = |-20| = 20
> LHA = 60 - 80 = -20 = 340
>
>> question 2 is this formula telling me to mutiply sin(dec) by sin(lat) and
>> then add it to multiplication of cos(dec) by cos(lat) by cos(dlo)
>
> Yes.  sin Hc = (sin dec * sin lat) + (cos dec* cos lat * by cos LHA)
>
> Order of operations:  Please excuse my dear aunt Sally.  PEMDAS
>
> P parenthesis
> E exponents
> M multiplication
> D division
> A addition
> S subtraction
>
> Do anything within the () first, as ordered above.
>
> No.  You need LHA, not dlo
>
> NOTE:  If you are careful to always subtract AP from GHA, most calculators
> will not mind if you feed it -20 instead of +340 as LHA.
>
>> question 3 if my methodlogy of question 2 is correct, then how do I get
>> the
>> result back to degrees and minutes for the answer Hc?
>
> Sine of the equation to the right of = is your answer in decimal degrees.
> Read the manual, do what it says to convert decimal degrees to ddd/mm/ss.
>
>> question 4 what is the difference in accuracy of HO 240 Vs Ho229 Vs
>> calculator?
>
> Your almanac explanation section will give you the range and probability
> of
> error for daily data.  Using almanac tables for dip, refraction,
> time-to-arc
> etc., could shift you an additional 0.1', maybe 0.2' worst case.
>
> 229 table errors for figuring d, v, d (adjustment to tabular Hc) and Z
> might
> be another 0.1' to 0.2" (rarely) over calculator. Most of the time these
> rounding errors will pretty well cancel out or be smaller than sextant
> accuracy (+/- 0.15 to 0.3') and operator/refraction/dip errors on the
> water.
>
> NOTE:  The calculator carries a lot of digits past the decimal point, that
> in theory are not significant digits anyway given the input.
>
> NOTE:  If you really want to be picky, find a v factor for the sun by
> taking
> the GHA difference for 24 or 48 hours and dividing by 24 or 48 and adding
> or
> subtracting from 15 (sun) to get a real angular speed.  Won't matter much
> at
> the 10-minutes-past the-hour mark, but can shift you 0.1' at the 40-50
> minute mark.
>
> I think 249 tables (solving the spherical triangle etc.) are less accurate
> than 229, but cannot speak to that from experience.  249 table books are
> smaller, but have limits on the stars you can use.
>
> Of any help?
>
> Bill
>
>
> >
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.392 / Virus Database: 268.5.2/329 - Release Date: 5/2/2006
>
>


--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To from this group, send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---