Hour angle

The solar zenith angle can be calculated in the following manner for any particular location (i.e., latitude and longitude), day of the year (dn), and time of day as described by Spencer (1971) and Madronich (1993). First, one needs to calculate what is known as the local hour angle (th), which is defined as the angle (in radians) between the meridian of the observer and that of the sun ... 

The local zenith angle / varies with time of day, season, geographic location. For example, at latitude 0 and a solar declination S, x varies with local hour angle, fh> according to (fh = 0 at local noon). 

The declination <5 of the sun, for 1st September, that appears in this equation, can be taken from tables presented by M. Iqbal [5.34] (5 = 8.51°. The hour angle ui is calculated from the local solar time ts, according to... 

Based on spherical trigonometry, a relationship can be derived connecting the solar zenith angle and the azimuthal angle 0o to the sun declination A, the latitude , and the hour angle H ... 

Solar Time - The period marked by successive crossing of the earth s meridian by the sun the hour angle of the sun at a point of observance (apparent time) is corrected to true (solar) time by taking into account the variation in the earth s orbit and rate of rotation. 

The solar zenith angle 6 necessary to calculate air mass in Eq. (3.4) can be obtained from the latitude q> (degree), solar declination 5 (radian), and hour angle h (radian). 

The correspondingly reduced Planck intensity should be representative of global conditions averaged over all latitudes and hour angles. 

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