Originally posted by Daemon Sin
Is it the range of radiation emitted by the sun?
The "range" of radiation of the sun extends WAY past that distance.
It(radiation) is said to affect the orbital trajectory of comets in the
Oort cloud, which may extend a trillion miles.
I did a calculation of the energy hitting the earth from Sirius a few
years ago and found it amounted to over 13 MEGAwatts spread out
over the whole surface of the earth. The numbers go like this:
you aim a light meter at Sirius (brightest star in the sky, 8 LY from
earth) and it says we get 9.8E-9 watts per square foot near earth.
For the purpose of calculation, the earth can be considered a
disk, so a disk roughly 8,000 miles in diameter is 64 million square
miles times 0.78 (PI R^2) is about 50 million square miles, times
640 (acres/square mile) times 43,600 (square feet in an acre) and
you come up with about 1.4E15 square feet of collecting area on earth
that would always face Sirius times by 9.8E-9 = 13+ Megawatts.
Of course that is orders of magnitude lower than the power from the
sun (126 w/ft^2 X 1.4E15 square feet= 1.8E17 watts hitting the earth
from the sun, about 150 BILLION times more than from Sirius
but it shows that power goes a long distance. 13 megawatts on the
earth from a distance of 8 Light Years.