Powerful green lasers has been one of the most exciting and most useful additions to astronomy in a long time.The reason why green lasers work so well as sky-pointers is two-fold. The beam becomes visible due to its colour because the sensitivity of the human eye peaks in the green-yellow. Secondly, the wavelength of green light is short enough so that the Earth’s atmosphere scatters it back to you, making the beam visible. The beam continues for several kilometers up in the sky, making it appear to you, as well as the as people around you, as if it is ‘touching’ the star you are pointing at. This is why a powerful green laser pointer is such a useful piece of astronomy gear since there is no ambiguity to which object you are referring to.
However, great care and responsibility is required when handeling such a dangerous “weapon” in the proximity of people. Never operate a laser of this power when there is the slightest chance of pointing it near someone’s eyes and never let a child play with it! And, however great the temptation, do not, under any circumstances point them at aircraft or passing cars! These are not toys! If you don’t use them responsibly, the authorities will ban them in no time (like they have done in a few countries already), so please be careful out there and don't spoil it for the rest of us!I got my first green laser back in 2006. First a 15mW and later a 35mW Wicked Laser - both which I tested then.
More recently (April 2010) I was sent a new generation 35mW SKYlasers to review.