Graphical Methods of Finding the Sun's Azimuth and Elevation

Abstract

Like Mr. R. S. Blicq (Journal 15,456) we have also been concerned in supplying details of the Sun's position to engineers on radar sites who use radiation from the Sun for, at present, two purposes:

(a) Measuring or checking the radiation pattern of the aerial in the vertical plane.

(b) Lining up the aerial in azimuth or elevation.

For these purposes the required accuracy of computation is usually about ±0°·1 in azimuth and elevation. Greater accuracy is never required, but less accuracy is sometimes adequate, up to ±1°.

We have found that graphical methods appeal most to engineers, and that even when a full table of values is supplied to them they prefer to display this information in graphical form. We have accordingly evolved a simple method of constructing graphs of elevation against time, and azimuth against time.

In order to achieve the required accuracy of ±0°·1 in elevation we have constructed a graticule of size 21 in. × 40 in. A skeleton version of this is shown in Fig. 1. The engineer has to know his latitude, and to find, from the Nautical Almanac or other source, the time of local noon (i.e. when the Sun is due south) and the mean declination, δ, of the Sun during the period of observation, which usually lasts up to three hours.