I'm pretty sure I'm not the only one who did this, but the first thing I did when I got my first laser pointer was go outside and point it at the moon. I'd stare and wonder if someone was up there, would they be able to see the little red light shining from the Earth?
Takayuki Ohira, creator of the MEGASTAR planetarium projector, recently conducted an experiment to test the limits of your generic laser pointer and posted the results on Twitter. He attached a class 1mW laser pointer to a telescope and pointed it at a building roughly 20km away to see if the light could be seen by the naked eye.
Check it out! It can!
Ohira was aided by Japanese astronaut Soichi Noguchi, who snapped a picture with his phone from the receiving end of the laser.
— 宇宙ニュース (@tx_spacenews) November 11, 2013
Ohira has warned that this is not something that people should be trying willy nilly. He specifically chose to conduct his experiment at night based on weather patterns and the air condition, and only did it after calculating the safe distance that the laser he was using could be viewed without harm to the retina, also taking time to properly calibrate his telescope.
At this point, it's also probably worth noting that last year alone, there have been over 3000 reported incidents of aeroplane pilots being disoriented by lasers being flashed into the cockpit — a crime punishable by prison time.
Ohira tweeted, "If it can be seen by the naked eye, it can be picked up by a sensor, so if you were to embed a signal in it, you could use it to communicate. It's optical communication so gigabit levels should be easy." After this success, Ohira is hoping to try from even further away.
This experiment was done with a 1mW laser. Think of how far one of those match-lighting 1500mW lasers can reach. My pointing-at-the-moon thing might not have been that crazy after all. Imagine that... Using a laser pointer to annoy cats from the moon...
大平貴之 [Twitter] レーザーポインターの光はどこまで見えるのか？ [Togetter] Laser pointer attacks on aeroplane pilots have jumped 1100% since 2005 [Quartz]