From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node16.html | 121 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 121 insertions(+) create mode 100644 src/slalib/sun67.htx/node16.html (limited to 'src/slalib/sun67.htx/node16.html') diff --git a/src/slalib/sun67.htx/node16.html b/src/slalib/sun67.htx/node16.html new file mode 100644 index 0000000..682e1dd --- /dev/null +++ b/src/slalib/sun67.htx/node16.html @@ -0,0 +1,121 @@ + + + + +SLA_AIRMAS - Air Mass + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_ALTAZ - Velocities etc. for Altazimuth Mount +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AFIN - Sexagesimal character string to angle +

+

+

SLA_AIRMAS - Air Mass +   +

+
+
ACTION: +
Air mass at given zenith distance (double precision). +
CALL: +
D = sla_AIRMAS (ZD) +

+

+
GIVEN: +
+
+ + + + + +
ZDDobserved zenith distance (radians)
+

+
RETURNED: +
+
+ + + + + +
sla_AIRMASDair mass (1 at zenith)
+

+
NOTES: +
+
1. +
The observed zenith distance referred to above means +``as affected by refraction''. +
2. +
The routine uses Hardie's (1962) polynomial fit to Bemporad's + data for the relative air mass, X, in units of thickness at the + zenith as tabulated by Schoenberg (1929). This is adequate for all + normal needs as it is accurate to better than + 0.1% up to X = 6.8 and better than 1% up to X = 10. + Bemporad's tabulated values are unlikely to be trustworthy + to such accuracy + because of variations in density, pressure and other + conditions in the atmosphere from those assumed in his work. +
3. +
The sign of the ZD is ignored. +
4. +
At zenith distances greater than about $\zeta = 87^{\circ}$ the + air mass is held constant to avoid arithmetic overflows. +
+

+
REFERENCES: +
+
1. +
Hardie, R.H., 1962, in Astronomical Techniques +ed. W.A. Hiltner, University of Chicago Press, p180. +
2. +
Schoenberg, E., 1929, Hdb. d. Ap., + Berlin, Julius Springer, 2, 268. +
+
+ +next + +up + +previous +
+ Next: SLA_ALTAZ - Velocities etc. for Altazimuth Mount +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AFIN - Sexagesimal character string to angle +

+

+

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +
+ + -- cgit