  The distribution of instellation at the top of a planet's atmosphere or
surface is usually calculated using the inverse-square law of radiation. This
is based on the assumption that the host star is far enough to be considered a
point-sized Lambertian source. This assumption, which works well for the solar
system planets and most exoplanets, must be revised for close-in exoplanets.
The objective of this work is to derive accurate instellation patterns for
close-in exoplanets, for which the effects of the spherical shape of the star
must be taken into account. First an analytical formula of the insolation as a
function of latitude was derived, taking the star and the planet as 3-D bodies,
and incorporating the limb darkening effects of the star. Then numerical
techniques were used to compute the distribution of the insolation on close-in
planets as a function of latitude for a wide range of stellar and planetary
properties.There are significant deviations in instellation values and their
distribution on close-in exoplanets, due in similar proportions to the physical
size of the star and stellar limb-darkening effects. The insolation at the
susbtellar point is always higher -- by as much as 21% for known exoplanets --
than the standard calculation. The substellar longitude of the terminator can
significantly extend on the nightside, from 90 degrees up to 110 degrees for
known exoplanets.
