O, we'll go no more a-roving
So late into the night,
Though the heart be still as loving,
And the Moon be still as bright. -Lord Byron
I am gazing at a color postcard of a beautiful oil painting, titled "Devonian Moon", created by my friend, the artist and amateur paleontologist Kristen Wyckhoff.
Kristen's painting depicts a giant, bright Moon shining through gauzelike clouds above the shoreline of a prehistoric sea. Kristen's speculative scene shows an upstate New York vista as it probably looked 380 million years ago.
Kristen's original 24" x 36" canvas imagines the Town of Gilboa, N.Y., southwest of Albany, as it looked during the impossibly remote Devonian Period of geologic time. This prehistoric scene is both alien and familiar to modern eyes, especially the appearance of a larger-than-normal full Moon.
During the construction of the Gilboa Dam and Schoharie Reservoir in the 1920s, the fossilized remains of Earth's earliest trees were uncovered; these towering trees were the ancestors of modern ferns and horsetails. The Gilboa forest grew near the shore of the vast, inland sea depicted by Kristen in "Devonian Moon".
The discovery of these world famous fossilized tree stumps and other plant parts made scientific news around the world. Today, several fossil stumps-members of the genus Eospermatopteris-may be observed at both the Gilboa Museum and at an outdoor display in front of the local post office.
Kristen was inspired to paint "Devonian Moon" when she first came across a reference about the Moon being closer to Earth during Devonian times.
"I learned that the Moon was half the distance closer to the Earth than it is today," she said. "That inspired me to paint 'Devonian Moon.'"
Kristen's depiction of our Moon, as it appeared millions of years before dinosaurs emerged on Earth, begs the question-what of our Moon in the distant future? Astronomers tell us that the Moon is slowly receding from Earth.
The Moon's orbit has been growing ever larger-estimated at a slow rate of 3.8 centimeters annually-since prehistoric times. Factor millions of years past and Luna was closer to Earth; but factor millions of years hence, and Luna will be farther from the Earth.
"Tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon's orbit-making the Moon's orbit bigger, but a bit paradoxically, the Moon actually moves slower," according to Dr. Britt Scharringhausen of Beloit College in Wisconsin. Scharringhausen is a professor of astronomy and physics.
"The Earth's rotation is slowing down because of this. One hundred years from now, the day will be 2 milliseconds longer than it is now. This same process took place billions of years ago, but the Moon was slowed down by the tides raised on it by the Earth. That's why the Moon always keeps the same face pointed toward the Earth. Because the Earth is so much larger than the Moon, this process, called tidal locking, took place very quickly, in a few tens of millions of years," she said.
While it won't be as large in the sky as it is today, the Moon of the far future will-with a nod to Lord Byron-be still as bright 500 million years hence.
Scharringhausen writes that just because the Moon is moving away from us inexorably, it will most certainly not recede so far from us that it will fade from naked-eye view.
"Changing the Moon's distance by a few percent won't have any significant effect on our ability to see it," she notes. "Changing the Moon's average distance by a few percent-which is what will happen over the next 500 million years or so-will similarly not prevent us from being able to see the Moon, and to see it quite easily with the unaided eye."
While the size of our future Moon will appear visibly smaller here on Earth, its surface brightness will be about the same as it appears right now.
"This is because although we will be receiving less total light from the Moon-since it is farther from Earth-that light will get concentrated into a smaller region of our field of view, and the two effects cancel out," Scharringhausen adds.
While the vastness and seeming indifference of the cosmos offers up scant surety, we can take small solace in knowing that hearts 500 million years hence-if they survive that long-will likely be still as loving, and the Moon will be about as bright. Note: To view Kristen Wyckhoff's painting "Devonian Moon", please see www.artbykristen.com (color postcards of this painting, suitable for framing, are also available). To learn more about the famous Gilboa tree fossils, see www.gilboafossils.org.
Lou Varricchio, M.Sc., lives in Vermont and was a science writer at the NASA Ames Research Center in California. He is a member of the NASA-JPL Solar System Ambassador program in Vermont and is a recipient of the U.S. Civil Air Patrol's Gen. Charles "Chuck" Yeager Achievement Award in Aerospace Education.