Asked by: Laurence Ager, Coulsdon
The light from the Sun follows an ‘inverse-square law’. So, if you’re twice as far from the Sun as the Earth, for example, you’ll receive one-quarter of the amount of light. Four times further away and you’ll receive one-sixteenth the amount.
The average distance of Pluto from the Sun is about 39 times that of the Earth’s. So, on average, the Sun on Pluto looks about 1,520 times fainter than it does on Earth. But this isn’t particularly faint. The full Moon is on average about 400,000 times fainter than the Sun. So, doing the maths, this means the Sun seen from Pluto is about 264 times brighter than the full Moon. This is about the amount of light you’d see on Earth when the Sun is around four degrees below the horizon, during ‘civil twilight’, which is more than enough to read by. Even on Pluto, looking directly at the Sun would probably be painful.