Galaxy will always appear dark

Hi again Hari.

Ignoring your planetary aspects for the moment, I would point out that we do not see light itself until it interacts with "something" and is reflected, or we are looking directly at the source. If our galaxy is "Mostly nothing" then there is "nothing" for the light to hit. So we would say "dark" even though there may be intense light coming from behind us if we didn't see it hit something in our visual field.

Brightness (illuminance) and darkness (Lack of illuminance) are the scale extreme conditions of the inverse square law for light intensity from a point source-see Wikipedia here:

http://en.wikipedia.org/wiki/Inverse-square_law

Now going back to your galactic question the total illuminance at any point in the galaxy would be a function of the distance from all of the point sources emitting light incident to that point and their respective fluxes. So if you had an Averaging light meter, you would notice very little change in the brightness available in space until you got VERY much nearer to a source of light.

Think candles scattered over miles in a very large desert. at night. No moon.

(Inverse square law was an is important thing to be mastered by anyone trying to do extreme closeup photography using bellows, extension tubes, or microscopes.With film. And no computers. To assure adequate exposure of chemical films.)

milo

Hi haricool,

Since galaxies are made up of millions to several billions of suns (stars), they will always appear light to us. However, due to their distance, they may not give us as much light as a single star in our galaxy. Does this answer your question?

-S

While any planet orbiting a star will have a dark side and a bright side not all planets rotate with relation to their star. Therefore some planets have a permanent night side and day side

I am not sure I understand your question. But the reason the sky looks blue in the 'daytime' is the higher frequency light (ie blue, violet) refracts off the earths atmosphere and scatters. The lower frequency light penetrates the atmosphere better. I think you can google '4th power scattering law' for a better explanation.