Beam divergence (both axes)? Beam diameter at aperture? Atmospheric conditions?If I focus my 2w 445nm laser to infinity, how many km or miles can the beam be visble or the dot?
You likely wouldn't actually see the dot or beam at that distance though, it'd only be visible if the beam hit your eye directly.
Yes, if/when ever I am thinking of pointing a laser at a star I 1st look and listen for aircraft and I don't take any chances, if an airplane is off to the side and flying away from my star I still wait until it's out of my sight, also everyone should know that helicopters can pop up over a tree line pretty quickly without much notice depending on the level of background noise so I suggest people always look and listen 1st before pointing to the sky.@RedCowboy thanks for chiming in and to be clear the link I posted ISS Laser Flash is from Laser Pointer Safety. And at the bottom of the article it also clearly states "LaserPointerSafety.com does not recommend that the general public try to replicate this experiment, by aiming lasers into the sky at the space station or any moving dot in the sky. In fact, for aiming at stars, low-powered lasers should be used (ideally 5 mW or less) and you should circle a star instead of pointing right at it, in case the “star” is really a slow-moving airplane. More info is on our Tips for outdoor use page. "
As there are other links about this experiment out there- such as the one you posted, that do not have the same disclaimer as the one mentioned in the Laser Pointer Safety link that I posted, it is still worth while to point this aspect out.