Mars does a disappearing act in the early morning sky on February 18. But not to worry, it's just hiding behind the moon, as Hal explains on this week's Looking Up. We’ve talked before about how the planets revolve around the Sun in pretty much a flat plane that is roughly circular. And remember too that the moons going around the planets in the Solar System are also going around in that same basic plane. That means that every now and then, from a particular observer’s point of view, planets and