All four Galilean moons are bright enough that they could, if they were farther away from Jupiter, be seen without a telescope. They have apparent magnitudes between 4.6 and 5.6 when Jupiter is in opposition with the Sun, and about one unit of magnitude dimmer when Jupiter is in conjunction. The main thing that is hard in observing them is due to the fact that they are very close to Jupiter, and are masked by its brightness. Their maximum angular separations from Jupiter are between 2 and 8 minutes of arc, close to the limit of human visual acuity. Ganymede and Callisto, at their maximum separation, are the likeliest targets for possible naked-eye observation. The easiest way to observe them is to cover Jupiter with an object, e.g. a tree limb or a power line that is perpendicular to the plane of moons' orbits.