Bill Bard writes: >In Mike McCants QUICKSAT.MAG and Ted Molczan N2L files, the magnitude >data for some/all of the sats are different. >Ted's data is specified for 1000 km 50% illuminated, Mike's 1000 km 100% >illuminated. To convert from 50% to 100%, ... stdmag(50%) - stdmag(100%) = 0.8 I. e., from that difference in definition, one would expect Ted's intrinsic magnitude to be 0.8 magitudes larger (fainter) than mine. >Comparing the data between the two files, the differences is greater than >that. For instance, Mike's file gives Vanguard 1's mag as 8.0, Ted's 12.4. >I'm just trying to understand the magnitude data. What am I missing? You are (and I was too until Ted and I very recently communicated about this) missing the fact that Ted is defining his intrinsic magnitude as a "mean" magnitude and I am defining my intrinsic magnitude as a "maximum" magnitude. So this means that Ted is "tilting" a cylinder to compute the effective average area visible and I am reporting a maximum magnitude which would normally be seen when the cylinder is at its maximum observable size. This difference in definition can easily explain 1 magnitude of difference in "intrinsic magnitude". In the past, Ted's file had only "computed" (from the size values) intrinsic magnitudes. Such a computed magnitude also must assume some sort of reflectance value. This is normally stated in the form: a one square meter object with 40% reflectance will be magnitude 6.0 (for example) at a range of 1000Km. My intrinsic magnitudes are based on my own (admittedly imperfect) observations. So if a given object is white or if (like Vanguard I) it is "shiny" and has a specular reflection that is greater than its diffuse reflection, then my observed intrinsic magnitude may be 1 or 2 or 3 magnitudes brighter than what would be expected from a 40% diffuse reflectance. Or, if I repeatedly observe that a "J" object has stabilized with one end pointing toward the earth, I may decide that its intrinsic magnitude is now 6.0 instead of a more normal 4.0 for a cylinder that is oriented for maximum reflectance. Now that Ted has changed a number of objects to "observed mean magnitude", there are a number of questions about how that value was derived and what it really means. But the bottom line is: If an object is observed to be tumbling and varies by 2 magnitudes, my intrinsic magnitude is supposed to predict its maximum brightness and Ted's intrinsic magnitude is supposed to predict its mean brightness and the latter is 1 magnitude fainter than the former. Mike McCants mikem@fc.net