Let the sun’s brightness on Earth’s surface be I,
The brightness the sun appears to be if the sun were four times farther from Earth will be （1/16）I.
根据：
The intensity (or illuminance or irradiance) of light or other linear waves radiating from a point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source; so an object (of the same size) twice as far away,receives only one-quarter the energy (in the same time period).