People recommending 30 - 50 mW greens for astronomy usually just have no idea what astronomy is about. Do you guys have ANY idea why dedicated astronomy lasers are ALL in the 3-5 mW range? Did you read the Z-bolt blurb that their 5 mW greenies are even LPM'ed and certified to be of NO MORE than 5mW??? Do you have ANY idea why a company puts that much effort into offering lasers that are of such low power in a world where laser nuts areare yelling about 3W devices?
I'll tell you why :
Green lasers over 5 mW are useless for astronomy pointing purposes. Anything over 5 mW will destroy the dark-adaptation of the human eye. A true 5 mW green is very visible in dark sky to the dark adapted eye. People who are serious about the astronomy hobby will tell you that even 5 mW is to strong, as most of us astronomers prefer a 1-2 mW green. All you need is a thin guideline of light into the sky that won't affect your vision on weak stars. If you can barely see it, that will be just bright enough.
Darkness adaptation is a process that takes over 20 minutes and it allows your eyes to see much fainter objects in very low light conditions. Dark adaptation is easily destroyed by even a weak light source, like a distant headlight of a car, or a laser beam that is to bright.
In astronomy, dark adaptation is THE most important part of your equipment. Without it, you won't be able to see a thing through a telescope (except for bright objects like the moon and the planets). Galaxies and nebulae that look like dim smudges to the unadapted eye are wonderfully detailed and extended sky objects once you are fully dark adapted.
There is no point in using a laser of which even looking alongside the beam will instantly destroy your adaptation. There's even more to that : looking along the beam of a 50 mW laser will hurt to the adapted eye. It is not even pointless, it is insane, it is dangerous, it is foolish. It is plain stupidity.
And you can trust on my maturity in this matter. I'm into astronomy for over 35 years.