The Moon has an especially close encounter with the planet Mars tonight. They climb into good view by around 10:30 or 11 p.m. Mars looks like a brilliant star. At its closest, it’ll be less than one degree from the Moon — about the width of a pencil held at arm’s length.
From much of South America, the encounter will be even closer: The Moon will pass in front of Mars, blocking it from view.
Such an event is called an occultation. The Moon will “occult” Mars — from a Latin word that means “to hide.”
Occultations of Mars are possible because both Mars and the Moon stay close to the ecliptic — the Sun’s path across the sky. But occultations don’t occur every time the Moon and Mars meet up.
That’s because the paths of both worlds are tilted a bit. Mars’s orbit is tilted by about two degrees. That means it can wander two degrees away from the ecliptic. The Moon’s orbit around Earth is tilted by about five degrees. So the Moon can move a little farther from the ecliptic.
As a result, the geometry has to be just right for the Moon to occult the Red Planet — as it does tonight.
Incidentally, Mars is getting a little bit brighter by the day now. It’ll pass closest to Earth in about a month, when it’ll shine at its brightest. Right now, only the Moon and the planets Venus and Jupiter outshine it. At its peak, it’ll surpass Jupiter — shining as the third-brightest object in all the night sky.