With the increasing popularity of high power green laser pointers
Very simply laser beams are very concentrated and narrow beams of light and lasers can have a range measured in tens of kilometers
. A high power green laser pointer may have a range of 20 to 30 kilometers but it will not have any power or be dangerous at this range. Even the best quality lasers will have a beam that grows in size by 10cm for every 100 meters. By the time the laser beam has covered 1 kilometer, the beam will be the size of a door way and will be incapable of causing any damage or harm.
Green laser pointers not red, blue or orange laser pointers are the main lasers pointed at aircraft because green is much more visible to the human eye than the other colors. The other reason is blue lasers and orange lasers are too expensive and relatively low powered to have wide spread use.
In summary
For the laser hobbyist who does not deliberately target an aircraft, green laser pointers are safe to use out doors at night. A good precaution when pointing lasers at the sky is to first check the sky to make sure it is free of aircraft and avoid using green laser pointers around airports.
For people thinking of pointing green laser pointers, it is Federal offence in the USA and rightly so. Lasers are very easy to track and offenders will face large fines and significant jail time. Pointing lasers at aircraft is also a serious criminal offence in most other countries.
With the increasing popularity of high power green laser pointers