Lacking any formal "Star" rating system, here's mine on a 5-Star scale. A 1 or 2 Star Scientist (if active in research) would likely be a person with only a Master of Science advanced degree. A person with only a Bachelor of Science degree might also be among those categories. Those folks often do find employment as lab technicians but generally do not run their own independent research programs. Three star and higher would likely require at least a Ph.D. in a science discipline such as Chemistry, Physics, Geology, Biology, Genetics, etc., plus a record of published research in peer-reviewed journals. Books would not count in that tally. Those folks often do run their own independent research programs. In that context, they might therefore be regarded as professional scientists, as opposed to amateur ones (no negative connotation intended).