
251Fundamentals of Solar Radiation
© 2008 Taylor & Francis Group, LLC
Capricorn (23.45°S) are at the extreme latitudes where the sun is overhead at least once a
year, as shown in Figure 5.6. The Arctic and Antarctic circles are dened as those latitudes
above which the sun does not rise above the horizon plane at least once per year. They are
located, respectively, at 66½°N and 66½°S. Declinations north of the equator (summer in
the northern hemisphere) are positive; those south, negative. The solar declination may be
estimated by the following relation*:
δ
s
n
=°
+
°
23 45
360 284
.sin
)(
(5.23)
*
A more accurate relation is sin δ
s
= sin(23.