If you’re a full moon watcher, tonight’s your night. The Full Buck Moon rises around sunset in the eastern sky and will light your path till tomorrow’s sunrise. Yesterday evening while finishing up mowing the lawn after sunset, I turned a corner and glimpsed a light in the distance. Since I wasn’t expecting it, I was pleasantly surprised to see it was the moon.
The name refers to the time when those little antler nubs first poke out of a male deer’s head. Other names for July’s full moon are Thunder Moon and Hay Moon. To see tonight’s moonrise, click HERE to find when it happens for your location. Be sure to pick the second moonrise time shown, not the “preceding day” time.
Rising’s a funny thing. The full moon appears to lift itself from the horizon and gradually travel in an arc from east to west, setting around the same time the sun rises tomorrow morning.
Of course, the moon’s really getting a free ride thanks to our rotating Earth. As the planet turns, your city and its moongazing inhabitants are gradually turned to face the moon at some time in the evening. The moment its shiny orange disk crests the horizon we pronounce it moonrise.
Meanwhile, the Earth keeps rotating until the moon is directly (more or less) above your city; it finally sets when you’ve rotated far enough for the curvature of the Earth to block the moon from view.
But the moon’s a bit of a sneak with moves of its own, which it employs every night to counter Earth’s bully-like rotation. As you gaze at tonight’s moonrise, keep in mind that that big bright ball is fighting a losing battle.
The moon revolves around the Earth once every 27.3 days from west to east in the sky. That’s slow enough that you and I don’t usually notice, but every hour that passes, the moon moves its own diameter (1/2 degree) to the east traveling at an average speed of 2,300 mph (3,700 km/hr).
Sorry Charlie. That’s not fast enough to counter Earth’s much more rapid rotation, which as we saw earlier, moves the moon across the sky from east to west during the night.
So Earth wins this game of cosmic arm wrestling. But does it? All those 1/2 degree increments accumulate over the hours. By tomorrow night, they’ll amount to 12 degrees or more than a fist held at arm’s length against the sky. Since the moon will be a fist further east, another hour of Earth-rotation will be needed to carry it back up to the horizon. That’s why the moon rises about an hour later every night.
So in the end, our favorite satellite can celebrate at least minor victory, don’t you think?