Best Answer:
Outside Earth's atmosphere, the Solar flux is 1370 Watts per square metre, for a surface placed perpendicular to the direction of the sunrays.
The flux varies inversely proportional to the square of the distance.
Earth's average distance from the Sun is 1 astronomical unit (AU).
Jupiter's average distance from the Sun is 5.2 AU
Solar flux at Jupiter = 1370 * (1/5.2)^2 = 1370 / 27 = 50.66 Watts/m^2
The trick I use to see how much is intercepted by the planet, is to use the "cross-section" of the planet - the area of a circle, with the same radius as the planet:
Radius of Jupiter (in metres) = 142,980,000
Cross-section = pi * R^2 = 6.422*10^16 m^2
Multiply that by the flux at Jupiter:
50.66 W/m^2 * 6.422*10^16 m^2 = 3.25*10^18 W
In "normal" numbers:
3 250 000 000 000 000 000 W (watts)
or
3 250 000 000 000 MW (megawatts)
3 250 000 000 GW (gigawatts, where both "g" are hard)
3 250 000 TW (terawatts)
3,250 PW (petawatts)
3.25 EW (exawatts)
Jupiter is bright because its clouds "bounce back" a lot of this sunlight without absorbing it (52% is bounced back).
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If all you are looking for is a ratio, compared to Earth, then it is the inverse of the distance, squared.
(1/5.2)^2 = 1/27
Jupiter receives 1/27 as much sunlight as Earth.
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