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About the cover

  D e s e r t   E x p o s u r e   November 2009

Rabbit Moon

Page: 3

OK so far, I thought. But as I dug deeper, things started getting complicated. The moon's orbit is elliptical, meaning the moon sometimes moves faster, sometimes slower. The elliptical shape of the orbit gets stretched and flattened because of the sun's gravitational pull on the moon. The tilt of the orbit varies slightly. Perigee and apogee slowly swap places. The tilted plane of the moon's orbit also rotates, like a top slowly spinning, in the opposite direction as the moon's orbit. The time for the "top" to spin around once is 18.6 years. Aha, at least I'd seen that number before.

TO LEARN MORE


"Astronomical Imagery and Numbers in Mimbres Pottery," by R. Robert Robbins, and Russell B. Westmoreland. The Astronomy Quarterly, 1991, Vol. 8, pp. 65-88.

"The Mythology of Classic Period Mimbres Painted Pottery Iconology: Evaluation of the Iconographic Interpretations," by Brian Sawyer Shaffer. A dissertation submitted to Texas A&M University in partial fulfillment of PhD requirements in anthropology, 2002.


"The Mystery of Chaco Canyon" (video), produced by Anna Sofaer of the Solstice Project, 1999. Bullfrog Films, Oley, PA.

"Mimbres Iconology: Analysis and Interpretation of Figurative Motifs," by Marc Thompson. PhD thesis, Archaeology Dept., University of Calgary, Alberta, Canada, 1999.

Lunar cycle simulation tools website: astro.unl.edu/classaction

Perigee/apogee calculator: www.fourmilab.ch/earthview

Calculator for dates and times of moon phases: www.usno.navy.mil/USNO

In my wanderings through cyberspace, I came across a wonderful website for astronomy education developed by the University of Nebraska-Lincoln (astro.unl.edu/classaction) It had several different animation tools for looking at phases of the moon, the moon's elliptical orbit, and how it moves in a wobbly Hula Hoop motion in relation to the earth. But I couldn't find anything that gave me a total picture of how all these different motions worked together.

My brain felt fried. I was beginning to understand why the moon was once thought to cause madness (the word "lunacy" was derived from luna, the Latin word for moon).

It was time to talk to an astronomer.



I paid a visit to Silver City astronomer Gary Emerson (see "Star Trek," November 2008) to see if he could help clear up my confusion.

"The moon's orbit is extremely complicated," he said. "People who get into this stuff are real wizards." That made me feel better, not being a wizard. No wonder I was befuddled.

He explained the 18-plus year cycle as the time it took for the moon at a certain phase to return to the same point with respect to the stars (for example, a full moon would be seen at the same place within a given constellation). It takes that long for sun, moon and earth to return to the same configuration in space. When the cycle repeats, the pattern of eclipses again fall close to the same calendar dates.

"One of the most incredible people," he recalled, was an Austrian astronomer named Theodor von Oppolzer (1841-1886) who in the late 1800s developed a canon of lunar and solar eclipses out to the 22nd century. "He would have had to calculate the moon's motion by longhand," Emerson said in awe. "No PCs, no calculators."

The moon's orbit is shifting gradually, Emerson added. Thousands of years from now, the full moon will rise in the north during the summer, rather than in the winter as it does now.

I mentioned Chaco Canyon and its connections to lunar cycles, and he agreed that the associations had been pretty well proven. "There's an incredible amount of moon lore and sky lore," he said. "Many cultures and tribes saw the moon as a grandmother or mother figure. The moon was always female, the sun male."

What did he personally see in the moon? He laughed at the question, having spent a year observing the moon in great detail as a student at New Mexico State University. Using state-of-the-art equipment, he and others studied the moon's surface for "transient activity" (e.g. volcanoes) in preparation for Apollo 11, the first manned flight to the moon. For him, the moon represented the beginning of his career in astronomy. Today, he continues to keep tabs on moon missions like the recent LCROSS mission, in which a rocket was crashed into a crater on the moon near its south pole in an attempt to find water in the form of ice.

Emerson said he still gets a kick out of watching the moon rise and set. At those times, "You can actually see the motion of the earth. If you can put yourself in that frame and think of yourself rotating, it's a really neat feeling."

 

Emerson loaned me a few more books, and I went back to studying lunar cycles. It turns out that there are several 18-to-19-year cycles. There's the Metonic 19-year cycle, over which lunar "moonths" and earth years work out evenly. There's the 18-year, 10 1/3-day cycle that Emerson described, the Saros, where sun, moon and earth come back to the same configuration in space and patterns of eclipses repeat. And there's the 18.6-year cycle of the moon's declination, within which the full moon moves from its "farthest farthest north" position to a minimum extreme and back again.

The moon's declination reached its maximum most recently in 2006, so now, only three years into the 18.6-year cycle, the moon still makes a wide swing from north to south within each "moonth." At full moon, it will be farthest north on Dec. 31. This full moon is also a "blue moon," the second one in a calendar month (the first is Dec. 2). All of December's full moons will appear large because they occur near the time when the moon's orbit brings it closest to the earth. The largest, brightest "perigee full moon" will occur on Jan. 30, 2010.



The moon's cycles were starting to make more sense to me, but I felt certain quite that I hadn't yet got it right. Scientists with computers could predict the moon's movements with enough precision to crash rockets into it or land astronauts on its surface. Ancient astronomers had aligned their buildings with lunar positions. I felt humbled by their knowledge of the moon's complexities. Mystified.

moon map

Author's rendition of a "Mimbres rabbit-man" in the setting moon.

I went back to observing the moon. I watched it as it changed phases and moved higher in the sky, then lower. I paid attention to how much later it rose each night, and to where it appeared on the horizon at moonrise. But the full moon itself proved hard to catch.

I was hoping to watch the full moon again when it was just rising, to see if the Man in the Moon had any more words of wisdom for me. I tried for several months, unsuccessfully. I'd look in the newspaper for the moonrise time and set my alarm, and the alarm wouldn't go off. When my timing was right, the rising moon was hidden behind clouds or haze. After practically sitting in my lap on that drive home from Tucson, the Man in the Moon seemed to want nothing more to do with me.

Feeling rebuffed, I turned my attention to the setting moon instead. Maybe it was from learning about all those lunar cycles, maybe it was from looking at Mimbres pottery, but I saw something totally new in the moon — a sort of Mimbres rabbit-man, in a mid-air bounce over a bicycle (see the drawing on this page). Please note that the wheels each have nine spokes.

What do you see in the moon?

What stories do you tell?


 


The author watches the moon from Silver City.

She is grateful to Marilyn Gendron, Dr. Cynthia Ann Bettison
and Gary Emerson for their assistance on this article.




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