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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Radians and Degrees
From: Paul Hirose
Date: 2020 Nov 1, 14:05 -0800
From: Paul Hirose
Date: 2020 Nov 1, 14:05 -0800
The ′ gauge mark on scale ST coincides with the number of minutes per radian (ca. 3440) on scale C. Thus, it helps you convert between minutes of arc and radians. And since the measure of a small angle in radians is also its sine and tangent at slide rule accuracy, you can get trig functions and their inverses. For example, Moon horizontal parallax is 59′. What is its distance? (Assume Earth radius = 6400 km.) 1. Set cursor to 59 on D. 2. Set the ′ mark to cursor. 3. Set cursor to 6400 km on D. 4. Read 373 000 km at cursor on C. Step 2 puts the C index at sin 59′ on D (about .01715). Step 3 calculates 6400 km / sin 59′. -- Paul Hirose http://sofajpl.com/
