(Mods, this may be a better fit in Outreach or some other forum; feel free to move it, but it arises from using a NVD.)
It looks like our scheduled outreach at our shared club / university observatory will happen tomorrow. I'll be using my 9.25 Evolution. At full dark, I plan to change over to a focal reducer and Mod 3, and spend the rest of the evening on M8, probably with a 7 or 12 nm H-a filter. I like to make visits to my 'scope at least somewhat educational.
I'd like to know what the average / typical density of hydrogen gas is in a nebula like M8, in terms at least some of the general public can maybe understand. I find that units like 'molecules per cubic meter' just go right past most folks (me included, often).
Is there some easily-grasped number like '1/10 the density of air at some XX altitude', or some other number and unit?