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airmass.c@ 1719

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Last change on this file since 1719 was 1719, checked in by cmv, 24 years ago
Adapted to version 3.5 xephem cmv 22/10/2001
File size: 805 bytes

Rev	Line
[1457]	1	#include <math.h>
	2
	3	#include "P_.h"
	4	#include "astro.h"
	5
	6	/* given apparent altitude find airmass.
	7	* R.H. Hardie, 1962, `Photoelectric Reductions', Chapter 8 of Astronomical
	8	* Techniques, W.A. Hiltner (Ed), Stars and Stellar Systems, II (University
	9	* of Chicago Press: Chicago), pp178-208.
	10	*/
	11	void
	12	airmass (aa, Xp)
	13	double aa; /* apparent altitude, rads */
	14	double Xp; / airmasses */
	15	{
	16	double sm1; /* secant zenith angle, minus 1 */
	17
	18	/* degenerate near or below horizon */
	19	if (aa < degrad(3.0))
	20	aa = degrad(3.0);
	21
	22	sm1 = 1.0/sin(aa) - 1.0;
	23	Xp = 1.0 + sm1(0.9981833 - sm1(0.002875 + 0.0008083sm1));
	24	}
	25
	26	/* For RCS Only -- Do Not Edit */
[1719]	27	static char rcsid[2] = {(char )rcsid, "@(#) $RCSfile: airmass.c,v $ $Date: 2001-10-22 12:08:26 $ $Revision: 1.2 $ $Name: not supported by cvs2svn $"};

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