The
average intensity of sunlight, falling at normal incidence just
outside the Earth’s atmosphere, varies
during the year due to the changing Earth-Sun
distance. We have to
show that the fractional yearly variation is given by
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Solution: Click For PDF Version Let a be the semi-major axis of the Earth’s elliptic orbit and e be the eccentricity of the orbit.The aphelion (the maximum distance of the Earth from the Sun) is given by
and the perihelion (the minimum distance of the Earth from the Sun) is given by
The maximum variation in intensity of the sunlight will therefore be
where
As average intensity of the sunlight at the Earth is given by
we note that
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approximately, where
e the eccentricity of the Earth’s elliptical orbit around the
Sun.
.
is a constant related to the Sun’s radiating power.
,
