I know there there has to be a simple answer to this, but I can't understand where it's at. Here is the question. Find the apparent magnitude of the Moon [Earth's] as seen from Mercury. Assume Mercury is 0.52 AU from the Moon and that Mercury sees the Moon fully [it's a full moon]. Okay, here is where my thinking lays. I'm going to be using M = m + 5 - 5log(d), where M = absolute magnitude of the Moon, m = apparent magnitude of Moon, and d = distance from Moon to Mercury in parsecs = 2.521×10^(-5) pc. But the problem I run into is M - I don't know it. I know that the absolute magnitude is the apparent magnitude measured at 10pc, but then I run into not knowing m. I guess I could use the apparent magnitude from Earth (≈-12.6), but when I plug that into the equation using the 10pc I get back -12.6 for the absolute magnitude and that does not work for me. I can only presume I am missing a piece of the puzzle and I don't know where it is. Any help you can offer me would be appreciated.