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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Azimuth Equation
From: T. Shanklin
Date: 2005 Oct 18, 23:12 -0700
From: T. Shanklin
Date: 2005 Oct 18, 23:12 -0700
I've been recently programming a TI-81 Calculator to do my sight reductions. Everything has been going swimmingly, getting closer and closer with my sights and shooting more stars- until the past week or so when the LHA of Altair at twilight became closer to 360 degrees. With all my fiddling, I've narrowed the problem and any accompanying possibly useful troubleshooting information down to this: The calculator will find Hc, but when it tries to calculate the azimuth, it sends back the error message "Math 04 Error". When I enter the equation and values manually as one equation I get the same message after pressing enter. Strangely it seems, I have found that when the Declination is South (that is- the dec value is negative) the error message does not occur and calculator works just fine. The error message only shows up when the LHA is 345 degrees or greater. I'm using the azimuth equation out of the Nautical Almanac: cos-1[(sinDec cosLat)-(cosDec cosLHA sinLat)/cosHc] To find Hc: sin-1[(sinDec sinLat)+(cosDec cosLHA cos Lat)] In entering the equation, if the Declination or latitude is South, or the Longitude is West, the value is negative. I am unable to figure this out; I've reached the end of my mathematical tether at this point. When I work it out manually one step at a time everything works out fine (e.g. calculate the sin Dec*cosLat, save that value, calc. cos Dec*cosLHA...) Does anyone have any clue as to why this is happening? Like I said, I had no problems whatsoever until the LHA began to approach >345 degrees. One example from my recent sights during which the problem occured: Altair-10/13/05- 0157:28 GMT LHA= 349.9983333 Dec= N8.885 Lat=N38.563 Todd Shanklin ********************** _________________________________________________________________ Don�t just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/