When you shine a flashlight into sky, how far does the light travel?

Question

When you shine a flashlight into sky, how far does the light travel?

Answer 1

wow, i've always wondered this. Good question!  =]

Answer 2

Depends on the atmospheric conditions.  The light would travel some distance, but would at some point get diffracted and deflected by the atmosphere so that it never even leaves the planet.  Eventually, the various photons would probably get absorbed by a non-reflective substance.

Answer 3

The light will travel until it is absorbed by something. Dust in the atmosphere, dust in outer space, a planet, a moon whatever. If it does not run into an absorbing material, the photons will continue indefinitely, decaying in intensity as the beam diverges, but never quite reaching zero intensity.

Astrobuf

Answer 4

depends on what kind of flashlight you have.

most regular flashlights cant reach as far as a flying airplane....soooo it all depends.

Answer 5

Until it becomes undetectable either by spreading, by scattering or by having its energy absorbed by dust and air.   The simplest measure is to aim it horizontally - over the relatively small distances the beam travels, if you can make it out shining on a wall, aim it further.  One of the reasons that lasers astonish us is that the beam is so coherant that it spreads very little, so we see the red dot much further than we see a light beam.  The flashlight beam never gets high enough in the atmosphere for the thinning air to make a difference on the distance.