A collaborative work of celestial art. Inexpensive, yet surprisingly powerful laser pointing devices have become ubiquitous in America. Millions of people own such a device.
Laser light stays coherent over vast distances, the beams spreading very little.
In theory, even a single laser pointer could reach the Moon. The idea behind Paint the Moon is to organize millions of people in North America to try and shine their laser pointers on one area of the Moon at one time, to see if we can create a temporary visible field of color on our nearest celestial neighbor. I honestly don't know. I'm a writer and an artist, not a scientist. But I think it could work, in theory.