Rayleigh scattering There is a citation needed at the claim that Rayleigh scattering can be seen I just did some research on Rayleigh scattering in air I added some content to Rayleigh scattering The bottom line is that at atmospheric pressure Rayleigh scattering at 532 nm is about 10 5 per meter A 1 mW green laser has a luminous power of 0 6 lumen and hence rayleigh scattering is 6e 6 lumen per meter over a 2 mm beam a 0 002 m2 surface The beam will hence appear roughly as if it were illuminated at 6e 6 0 002 3 millilux which is comparable to a moonless clear night sky I should actually correct the number to deal with the angular distribution A dark adapted eye should be able to see this especially when you look along the beam which multiplies the apparent brightness by 1 sin theta where theta 0 deg means you look paralell to the beam Now I m not sure how to turn this original research into verifiable encyclopedic content t