THE INVERSE SQUARE LAW
Ever went somewhere like a quite dark street with only few working street lamps? Notice how the illuminated part of the ground radially decrease intensity? Or noticed that a campfire is less 'hot' when you are far from it? Ever wondered why?
Some might instantaneously shout "CUZ' AM FAR AWAY, DUH", which is not actually wrong, but, there is way more than that.
The same way you can't see/feel the waves generated by a pebble thrown 10 miles away from you in a calm sea, you can't hear someone more than 300m away or be illuminated by a street lamp from 20km...
The kinetic force of the pebble in the water creates waves that radially expand outwards through the medium (water surface), all waves behave the same way, as a consequence of our tridimensional space, these radii in a 3D medium like Space gradually expand outwards, BUT as far the number of particles (in the case of light, photons) still the same, these particles are spread out in larger and larger areas as distance increases.
Now you know that when you're away from the campfire, you're receiving less infrared light than being closer to it.
The amount of anything that spread in space is inversely propotional to the square of the distance you're measuring from the source.
Mathematically, using light as example:
LR = (LS / D²)
Where:
LR = Light Received
LS = Light from Source
D = Distance
Of course, result value is proportional to you unit of distance (m/mi/Km/AU) and your unit of measuring the 'thing', which is light or intensity of a force, it could be Joules, or Watts or a standard luminous parameter.
Let's calculate how much light reaches Venus.
Taking the Sun intensity as 1.
Taking the Light that reaches Earth from 1 AU is 1.
Venus orbits the Sun at ~0,73 AU.
Then we have:
LR = 1 / 0,73²
LR = 1 / 0,5329
LR = 1,876524676299493
Venus receives ~1,87x as much light as Earth.
Proportionally, if you move closer to the source by ~25% (almost like Venus), expect the intensity to rise up by ~75%, if you 50% the original distance away, then the final intensity is 400% the original.
If you double the distance, light will be 4x weaker, if you triple it, light is 9x weaker and so on.
- M. O. Valent, 12/04/2019
