Full Buck Moon Gets A Free Ride From Earth Tonight

Don’t miss the rising of July’s Full Buck Moon tonight. Credit: Bob King

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.

While you’re out moongazing tonight, you’ll notice how squished the moon appears near the horizon (left) compared to when it’s higher up. Earth’s atmosphere acts like a prism to refract or “lift” the bottom half of the moon into the top, giving it a flattened appearance. Credit: Bob King

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.

Earth’s rotation carries the full moon up from the horizon along Lake Superior in Duluth, Minn. In this moonrise sequence a photo was taken about once every 2 minutes. Credit: Bob King

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.

As Earth’s rotation makes the moon (and stars, sun, etc.) move from east to west, the moon is quietly – and slowly – moving counter to that direction to the tune of its own diameter per hour. Credit: cseligman.com

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?

4 Responses

  1. Edward M. Boll

    With the Moon moving rapidly north, that is what I love about Harvest Moon which rises only about 25 minutes later each night. I know that Harvest Moon is sometimes in October. But if Full Moon is around Sept. 19, whether it is or not I call it Harvest Moon. That is the Anniversary for my wife and I. This year, the Moon is Full or near Full on that date. And to boot, this year we have a close conjunction of Venus and Saturn. I have also been a Laurel and Hardy fan since 74. And I like Hardy’s singing of ”Shine on Harvest Moon”.

    1. astrobob

      Hi Edward,
      I’m a Laurel and Hardy fan too. My favorite scene: when the two dance to the song “At the Ball” in front of the cowboys in “Way out West”

  2. GD Boots

    The Buck moon is off by a month or two. I have a six pointer in my garden every night and he started nubbing in late may. How about a Velvet moon, referring to the velvet that covers the bucks antlers.

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