Celestia Forums

This thread got me wondering about something.

The illumination on a planet's surface in a multiple star in Celestia depends on the relative brightness of each star shining on it. As the example on page 2 of that thread shows, if the brightness of the two stars is equal at the planet then the surface will be illuminated equally. If one is a bit brighter than the other, then the illumination from the dimmer one is significantly reduced. If one is MUCH brighter than the other then the illumination from the dimmer one just plain disappears.

IIRC this was done to simulate the response that the human eye would have to the different brightnesses wasn't it? If that's the case, then why don't we do the same thing for the attenuation of light with the square of distance from the star? If we're accounting for the eye's response in one case shouldn't we do the same for all cases?

(or is that not why we do that for multiple systems?)

Sorry for the bump, but I really am rather curious about this. Or does nobody except Chris know the answer to this?

Only Chris can answer for sure. Statements by others are just opinion.

However, the topic of the reduction of illumination due to distance from the sun has been discussed frequently. The rationale for Celestia showing Mercury with the same brighness as Pluto is that the human eye automatically adapts to differences in overall ambient brightness. You would not see any appreciable differences in total illumination levels when visiting separate bodies close to or far from a light source.

However, you do see differences on the surface of an individual object when it is illuminated by more than one light source.