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airmass.c@ 3632

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Last change on this file since 3632 was 3477, checked in by cmv, 18 years ago
mise a jour Xephem 3.7.3 , cmv 25/03/2008
File size: 782 bytes

Rev	Line
[1457]	1	#include <math.h>
	2
	3	#include "astro.h"
	4
	5	/* given apparent altitude find airmass.
	6	* R.H. Hardie, 1962, `Photoelectric Reductions', Chapter 8 of Astronomical
	7	* Techniques, W.A. Hiltner (Ed), Stars and Stellar Systems, II (University
	8	* of Chicago Press: Chicago), pp178-208.
	9	*/
	10	void
[2551]	11	airmass (
	12	double aa, /* apparent altitude, rads */
	13	double Xp) / airmasses */
[1457]	14	{
	15	double sm1; /* secant zenith angle, minus 1 */
	16
	17	/* degenerate near or below horizon */
	18	if (aa < degrad(3.0))
	19	aa = degrad(3.0);
	20
	21	sm1 = 1.0/sin(aa) - 1.0;
	22	Xp = 1.0 + sm1(0.9981833 - sm1(0.002875 + 0.0008083sm1));
	23	}
	24
	25	/* For RCS Only -- Do Not Edit */
[3477]	26	static char rcsid[2] = {(char )rcsid, "@(#) $RCSfile: airmass.c,v $ $Date: 2008-03-25 17:45:09 $ $Revision: 1.7 $ $Name: not supported by cvs2svn $"};

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