The exact question I need to answer is 'Explain how you decided which moon was which?' and we are learning about Jupiters moons.
Answers (1)
By looking at them, they are quite easy to differentiate, usually the position is the easier way though, starting with the nearest to Jupiter and working our way outward;
Io is yellow and sulphurous.
Europa is mostly white with reddish brown cracks on the surface.
Ganymede is grey but mostly unmarked.
Callisto is grey also but has white marks at the site of impacts.