|
Size: 2148
Comment:
|
Size: 2103
Comment:
|
| Deletions are marked like this. | Additions are marked like this. |
| Line 9: | Line 9: |
| || Planet || Diameter || Distance || Intercepted || || || km || AU || fraction || |
|| Planet || Diameter km || Distance AU || Intercepted Fraction || |
Sunlight Intercepted by Planets
The vast majority of the sun's light will never intercept matter again. What fraction reaches the major and dwarf planets?
Given the diameter in km D, and the average distance from the sun in AU, the fraction intercepted by a round object object is:
(pi*D2/4)/(4*pi*(149598000*AU)2) = ( 1 / (16 * 1495980002)) * ( D / AU )2 = 2.793E-18 * ( D / AU )2
Planet |
Diameter km |
Distance AU |
Intercepted Fraction |
Mercury |
4878 |
0.39 |
4.37e-10 |
Venus |
12104 |
0.72 |
7.89e-10 |
Earth |
12756 |
1.00 |
3.15e-10 |
Mars |
6787 |
1.52 |
5.57e-11 |
Jupiter |
142800 |
5.20 |
2.11e-09 |
Saturn |
120000 |
9.54 |
4.42e-10 |
Uranus |
51118 |
19.18 |
1.98e-11 |
Neptune |
49528 |
30.06 |
7.58e-12 |
Dwarf Planet |
|
|
|
Ceres |
975 |
2.77 |
3.46e-13 |
Pluto |
2300 |
39.44 |
9.50e-15 |
Eris |
~2700 |
67.67 |
4.45e-15 |
Total |
4.17e-09 |
||
So, 99.99999958% of the Sun's light leaves the solar system. Half of the tiny fraction intercepted is by Jupiter, 19% by Venus, 11% by Saturn, 10% by Mercury, and 8% by Earth, with a tiny fraction of the tiny fraction intercepted by the other planets, dwarves, moons, asteroids, and Kuiper belt objects.
A hypothetical giant telescope mirror 100 meters across and 100 light years away might intercept 1.1E-32 of the Sun's output, about 4 microwatts. At that distance, the Sun would be magnitue 7.6, not quite visible to an unaided human eye. If intelligent life is rare, then chances are nobody would notice if we captured all the light. OTOH, a 50AU diameter infrared sphere would still be visible (and anomalous!) to a very distant astronomer with a large infrared telescope. Perhaps we should be looking for such objects.