How far could the ray from my laser pointer travel?

Question

At some clear and starry nites, I often point out the stars with my laser pointer. I wondered, how far does the ray travel? Does it ever reach the distance stars out there?

Answer 1

In the vacuum of space the light from your laser-pointer would, theoretically, travel forever -- except that outward pressure from the photons, from which the the light is composed, eventually disperse the laser's coherent-light beam.

Here on Earth, the energy in the beam is sapped, little by little, from collisions with the gas molecules in the air, as well as the dust particles and tiny water droplets suspended in it (remember that air is not invisible; it is merely transparent, and miles and miles of it add up, the same way that thin glass panes that seem to clear individually form a dark green opaque mass when stacked twenty thick), with all the energy scattered and absorbed.

Still, though your laser-pointer will not illuminate significantly beyond a range of 200-300 feet, its light is still intense enough to trigger the receptors in the retinas of observers a mile or two away. To them it will appear as just a tiny point of light.

PS: In the early 1960s NASA bounced a very powerful laser beam off the surface of the Moon, 238,000 miles away. The beam started out at the source less than a half-inch wide; by the time it struck the moon it was nearly a mile wide (and very faint) as a result of the pressure from the energetic photons (and some inevitable dispersal due to its passing through the Earth's atmosphere on the way to the Moon).

Answer 2

Just a thought: By the time the light from your laser travels the distance to the nearest stars, that star would have been traveling quite a distance as well. I wonder if the two would ever meet?

Answer 3

Unlike gas lasers the solid state lasers in a pointer require a lens for focusing - this is the limiting factor for the beam divergence. The lens is often just moulded plastic so not good.
Oh and I hope you don't live in "the land of the free" as people have been arrested for pointing lasers up as homeland security think you are practicing taking aircraft down.

Answer 4

there are many things i would like tou to imagine:

first of all if you were on a place as bright as the sun itself how would you be able to see a tinie winiee beam of a laser pointer

secondly by the time your beam reaches the point where you initially pointed (which is the star) the star would be somewhere far away from it.

Answer 5

Its unlikely that your pen point laser would be seen outside of the earths atmosphere due to atmospheric absorption! - dithering and scattering by dust particles in the upper layers of the atmosphere. But go outside of the atmosphere and your laser would go on forever! or until it hit something that absorbed it or scatted it!.

However if the emitted level of the laser is high enough and of the right wavelength then it would get through the atmosphere and most likely go on forever or until it was absorbed or scattered.

Answer 6

It's distance of reach is infinite.
Light as sound never stops, but becomes distorted and needs more and more sophisticated devices to record.
It will reach the stars, but probably take many light years, lifetimes, or eons to get there.
Calculate it out at the speed of light.

Answer 7

If it is unobstructed, it will go on forever. All light travels at 186,000 MPS, so yes, it will eventually reach the distant stars. Of course, it will be to faint to see.

Answer 8

Supposedly it goes on forever