I’m assuming there’s not enough light to reflect, so I’m just guessing that all I would be able to see was where it occluded stars. Yes/no? And, if I’ve interpreted correctly, Pluto and Charon are so tidally locked that Charon’s revolution around Pluto matches Plutos rotation on its own axis, so that (help me if I’m wrong), one side of Pluto would always “see” Charon in the same place in the sky (but varying depending upon exactly where you were located), and the other side would never see it at all.
No, you’d have no trouble at all perceiving Charon as a bright object.
Pluto averages about 40 astronomical units from the Sun, meaning the Sun shines only 1/160 as intensely there. Assuming that the albedo of Charon is comparable to that of the Moon, it would glow 1/160 as bright (before adjusting for size and distance) as our Moon.
This may not sound like much, but we have no trouble at all perceiving the earth-lit side of the crescent Moon from Earth, and the earthlit side is only about 1/10,000 as bright as the sunlit side.
Correct. Other than minor movement due to libration, Charon would hang motionless in the Plutonian sky–as would Pluto from Charon, as does the Earth from the Moon.
No. You can easily see Pluto through a telescope, visually. That means there’s enough light there to see things by. (Telescopes don’t amplify light, they just magnify things.)
In fact, the sun as seen from Pluto is about 300 times brighter than the full moon as seen from earth. That’s plenty of light.
That’s correct.
Of course, Charon will still go through the phases.
By the way, Charon’s apparent size in the sky would be about 3.5 degrees. That’s 7 times the diameter (or 50 times the area) of our moon as seen from earth.
D’oh, 40 squared is 1,600. Doesn’t change the argument, though–picture an object moderately brighter than the earthlit part of a crescent moon.
Of course, that only applies when Charon is in full phase. When it’s new, it would glow only with “Pluto-shine”, and at that point, I imagine you would perceive it only via occluded stars.
You might see the Pluto’s other moons, Nix and Hydra too.
Nitpick 1: Might have to qualify “easily” there - it’s not easy to find, and you need a good telescope and nice dark skies. And to make sure you’re looking at the right dot you need a very detailed star atlas. Photographs taken a week apart help too. But yes, under the right conditions Pluto is visible in a telescope. (Can’t say I’ve done it myself 
)
Nitpick 2: While ‘amplify’ would the the wrong word, telescopes absolutely do gather more light than your eyes can. That’s their primary function. Magnification is useless if you aren’t gathering enough light.
Combining the previously presented bits of data, Charon seen from Pluto would take up 50 times the sky area as the Moon seen from the Earth, but each portion would be illuminated only 1/1600 as intensely. Thus, if Charon has the same albedo (percentage of light reflected) as the Moon, it would be 1/32 as bright in any given phase.
You could have a look at this solar system simulator - there’s all sorts of settings you can use…
Sweet! Do you have suggestions on settings? Looks to me like “field of view” should be on 10 degrees to get a realistic size…
Point taken about it being difficult to find and requiring a large telescope. But only because it’s small, not because of low surface brightness.
My point was that a telescope cannot increase the apparent surface brightness of an object. At best it can provide an image that’s larger than the original, and with the same apparent surface brightness. If the target is too dim (low surface brightness) to see to begin with (e.g. Barnard’s Loop), no telescope can increase its brightness to where you can see it.
I’ve been caught by this mistake, too. The confusion comes from “point sources” like the stars. If you look at a star through a telescope, it won’t look any bigger than without the telescope, but it will look brighter. Really, though, there aren’t any true point sources: What’s really happening with that star is that it’s going from a really small angular size, and some surface brightness, to a larger but still very small angular size, and the same surface brightness. It’s only because the image, even magnified, is so small that you don’t realize the surface brightness is unchanged.
You mean before your eyeballs either freeze oe boil off? 
Using the simulator linked above I just took all the defaults the page loaded with. WIll someone tell me what that is chasing the earth? (SIRTF?)
Sorry for the hijack…
SIRTF is an astronomical satellite, better known as the Spitzer Space Telescope.
That’d be the Spitzer Space Telescope:
Cool, there’s a moon named after my family.
Long live the Hydras!
That can’t be true. We see light that bounced off the object in the direction of our pupil. Assuming that light hitting an object will on average be scattered evenly over a semisphere back, dependent on what percent of the surface area of that sphere is that intersects with your circular view port, the surface brightness will appear greater or less. Obviously the true surface brightness won’t have changed, but it should appear brighter. If you look through a pinhole, the world will appear darker, and if you look through binoculars it can appear brighter.
Yes, the light from a given patch of illuminated surface will be reduced by distance. But each “pixel” of your eye would also be seeing a larger area, so the apparent surface brightness (watt per square degree) remains the same.
Of course it’s possible for a telescope to reduce apparent surface brightness (e.g. your pinhole example). All I said is that it can at best preserve the same apparent brightness.
We’ve had a similar discussion in these threads:
Can large-objective binoculars double as night scopes?
Passive night vision goggles?