perigee

As the moon wheels around Earth every 28 days and shows us a progressively greater and then stingier slice of its sun-lightened face, the distance between the moon and Earth changes, too. At the nearest point along its egg-shaped orbit, its perigee, the moon may be 26,000 miles closer to us than it is at its far point.

Conjunctions of I and II [Io and Europa] occur when they are near perigee and apogee respectively; conjunctions of II and III [Europa and Ganymede] occur when II [Europa] is near perigee.