# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Fw: Chichester's Calculations ( Sine-Cosine method)**

**From:**Gary LaPook

**Date:**2008 Dec 15, 03:13 -0800

I am attaching an example of the same computation done with Weems Line Of Position Book which provides the shortest solution of all the tabular methods. This requires only three entries to the tables to find Hc and then the azimuth is found by Rust's diagram. The example requires only two pages because two of the values are found on one page. See attached files. gl Gary J. LaPook wrote: > I also decided to work the problem using H.O. 208, Dreisonstok for > comparison. This method requires four table entries taking out eight > values and four additions. > > See attached example and H.O. 208 excerpts. > > gl > > Gary LaPook wrote: > >> I also decided to work Chichester's example using my Bygrave Slide Rule >> since Chichester used one of these when he flew his Gypsy Moth airplane >> from New Zealand to Australia in 1931. I came up with an Hc of 46º 26', >> Az of 57º10' the same as Chichester got. I have attached this computation. >> >> gl >> >> >> Gary J. LaPook wrote: >> >> >>> I decided to work the same example using the standard Sine- Cosine >>> method to compare it to the Haversine-Cosine method. I discovered that >>> it takes fewer table entries and additions than does the Haversine >>> method so I do not know why that method became the prefered method, any >>> ideas? >>> >>> I am posting and example of this computation. I am also attaching a PDF >>> of it to ensure that the format doesn't become corrupted. >>> >>> The normal formulas for computing Hc and azimuth are: >>> >>> sin Hc = sin Lat sin Dec + cos Lat cos Dec cos LHA >>> >>> and >>> >>> sin Z = (sin LHA cos Dec)/ cos Hc >>> >>> rearranged to the more convenient >>> sin Z = sin LHA cos Dec sec Hc >>> >>> These can be solved using logarithms using this format: >>> >>> >>> >>> >>> >> >> >> > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---