NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Slide Rule Azimuth
From: Gary LaPook
Date: 2009 May 30, 05:12 -0700
From: Gary LaPook
Date: 2009 May 30, 05:12 -0700
That is the formula that I have used for years for calculating azimuth. You can find it in Bowditch. George has pointed out that it gets ambiguous near east and west but it is not a problem in real life and is quick and easy to do on a calculator or slide rule. For those rare cases near east or west another formula could be use. The Az calculated with this formula is between zero and ninety degrees so you have to figure what quadrant you are in and convert to Zn but this is also not a problem in real life since you know the approximate direction when you pointed your sextant. See: http://groups.google.com/group/NavList/browse_thread/thread/af4f15cde5075f8f/058fe8755eeaca37?hl=en&lnk=gst&q=lapook+cosine#058fe8755eeaca37 http://groups.google.com/group/NavList/browse_thread/thread/529edc05997d59d7/e002865149e31596?hl=en&lnk=gst&q=lapook+cosine#e002865149e31596 gl Greg Rudzinski wrote: > An interesting azimuth formula presented by H.H. Shufeldt in his book > SLIDE RULE FOR THE MARINER (pg. 77) > > Azimuth = INV SIN of COS declination Sin meridian angle divided by > COS altitude ( Ho or Hc ) > > Shufeldt states that Ho or Hc altitudes can be used. The INV SIN > result is added or subtracted from 360 or 180 degrees depending on > orientation. > > An alternate arrangement for the formula: > > Azimuth = INV SIN of SEC altitude COS declination SIN meridian angle > > I like the expediency of this formula but it does suffer from > inadequate slide rule scale resolution for azimuths approaching 270 > or 90 degrees. A trick to by-pass this problem for a sun observation > would be to directly observe a corrected bearing of the sun (which > should be low in the sky) for use as an altitude intercept azimuth. > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---