AlexT wrote:
Reading through various articles about the upcoming launch of the New
Horizon probe I did not manage to locate any solid information about
the amount of energy & light available from the Sun on Pluto.

At the top of the Earth's atmosphere, the "solar constant"
(= incident power-per-unit-area from the sun across all wavelengths)
is 1340 Watts/m^2.

Pluto's mean distance from the sun is 39.4 times that of the Earth.
[The orbit is rather elliptical, so this distance
changes as Pluto orbits the Sun. At its closest
(most recently in Sept 1989), Pluto's distance from
the Sun is "only" 29.6 AUs (where an AU, "astronomical
unit", is the Earth's mean distance from the Sun);
at its farthest (which will next happen in the year
2113) Pluto's distance from the Sun is 49.3 AUs.]

The solar power-per-unit-area falls as the inverse square of the
distance from the sun, so at a distance of 39.4 times that of the
sun, the incident solar power-per-unit-area at Pluto is 0.86 Watt/m^2.
Right now Pluto is only 16 years past its perihelion (the point in
its orbit where it's closest to the Sun), so if we use the perihelion
distance of 29.6 AUs, that gives a solar power-per-unit-area of
1.5 Watt/m^2.

For comparison, this latter power-per-unit-area is equal to that
of a 100 Watt light bulb at a distance of 2.3 meters. That's
a bit dim for office lighting, but still plenty to read by.

ciao,

--
-- "Jonathan Thornburg -- remove -animal to reply"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
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