I read in a work of fiction than in Pluto the Sun is nothing more than a very bright star in the sky but that it is still strong enough to cast a shadow of someone standing on Pluto’s surface. Is this true? If not, where is the farthest it would?
You would have a shadow, but it might not be very distinct (since everything would be pretty dark). It gets about 1/1000th the sunlight Earth does. While dim, that’s still 450x brighter than Earth’s moon appears to us.
I’m not sure where you’d stop having a shadow… it would probably be at the point where average starlight was more or less equivalent to the sun’s. Since stars are millions of times fainter, you’d have to go pretty far out.
Well, the moon can most definitely cast visible shadows. 450 times brighter should create very distinct shadows.
At its maximum brightness, Venus can cast shadows (on Earth).
http://www.gsfc.nasa.gov/gsfc/educ/science/2000/02-01-01.htm
Definitely a shadow thrower.
Also note that the shadows on Pluto would be somewhat faded, but they’d be extremely sharp. The fuzziness you see around shadows, especially those cast by objects far away, is caused by the angular size of the Sun in the sky. Since the angular size of the Sun is much smaller from Pluto, the shadows will therefore be sharper.
Venus makes a good marker for the limit of brightness at which an object will cast shadows visible to the human eye. The Sun would be as bright as Venus if viewed from 28,840 A.U.'s–about a tenth of the distance to Alpha Centauri.
Amazing.