Apparent Magnitude

From Slackerpedia Galactica

The brightness of a star as measured by our eyes. It's a useful quantity for those who go out and look at stars on occasion, but not so useful for people doing physics. The luminosity of a star is what's interesting to physicists, and since the brightness of a star depends upon its intrinsic luminosity and its distance, you have to know the distance to get useful physical information from the apparent magnitude. And it's hard to figure out the distance.