Moon in the Balance

I am torn.

As an amateur astronomer, I must arrange my observing life around avoidance of the Moon; wait impatiently for it to set; nervously watch the eastern horizon for its arrival; hide from it behind trees, rock outcroppings, vehicles, and outhouses; wail and curse it when it appears. Let’s face it, that old incandescent Moon is the bane of every hunter of "faint fuzzies": deep-sky objects pursued with telescopes, binoculars, and much lurching about in pitch-dark places.

Faint Fuzzies: Hickson 44 galaxy group

As a human being, though, I must marvel at the Moon and think how lucky we are. We have a natural satellite that shows us, through its phases, that it revolves around us. When it covers the Sun during a solar eclipse or moves into the Earth’s shadow during a lunar eclipse, we have a glimpse into the clockwork of the universe. We have a naked-eye view of the surface of another solar system body. We even have a cosmic timepiece that ticks along reliably enough to give us the basis for our system of calendar months. (Did you know the word month is derived from the Old English word for moon, mona?)

The approach of Full Moon on Friday the 18th has me pondering what I’d do if given the power to choose between keeping the Moon or banishing it forever. A giddy free-for-all of deep-sky diving, unfettered by the lunar cycle, versus a glowing orb that has inspired humans throughout history to pen poems, create art, write songs, do science, and pitch woo. The everlasting happiness and gratitude of my stargazing brethren versus the artistic, scientific, and romantic outpourings of the human race. It would be a tough call.

There are some practical reasons to keep the Moon. In a previous post, I discussed precession, the slight wobble of Earth’s axis. This wobble is caused by gravitational tugging by both the Sun and the Moon. If the Moon were removed from the picture, Earth’s wobble would destabilize, becoming more erratic and pronounced. This would most likely result in dramatic climate changes.

Image courtesy of PDPhoto.org

Another reason to hang on to our satellite has to do with tides. The combined gravitational pull of Sun and Moon causes the cyclical rise and fall of Earth’s oceans, the tides. Although the removal of just the Moon would not eliminate the tides, it would certainly disrupt them. The feeding and breeding activities of various marine and shore creatures could be severely impacted.

Even if we subtract these practical considerations from the equation, ultimately I think I’d miss the Moon if it were gone. I’d miss how the waxing crescent looks like a big, happy tangerine slice before it sets, and a crescent in the clouds like a shark fin slicing through seafoam. I’d miss that loopy Moon illusion that makes the rising Full Moon look unnaturally big. I’d recall the lunar eclipses I’ve watched and how the Moon in Earth’s shadow always turned red--sometimes russet, sometimes scarlet. I’d miss the gasps and whoops that a telescopic view of the Moon’s crater-pocked surface elicits at public astronomy events. I’d miss my own telescopic tramps across the Moon and moments of discovery. Strangely, I think I’d even miss the collective groan that rumbles across a star party’s observing field when the Moon bobs up in the east.

Observing field at a star party

So, at the end of the day, with all that fateful power at my fingertips, I’d have to give La Luna the thumbs-up. Of course, I’d also have to change my name, move out of state, and never show my face at another star party. Anywhere. Perhaps we should keep this just between us.

Top Ten Moon Myths

As you gaze at this week’s big moon--and frolic in the light of the Full Moon on Sunday, April 20--ponder my picks for Numbers 10 through 6 of the top ten moon myths of all time:

10) The Moon’s surface is completely smooth. Early science through the time of the Renaissance was based upon the teachings of the influential Greek philosopher Aristotle. According to his worldview, the Moon was a perfect sphere with a perfectly smooth surface. The invention of the telescope in the 17th century blasted that myth into oblivion. When the pioneering Italian astronomer Galileo turned his homemade telescope skyward in 1609, he discovered that the Moon was pockmarked with craters and crisscrossed with mountains and ridges.

Unfortunately, Galileo misinterpreted one type of lunar feature he saw: the dark, basalt-filled craters. He thought they were water features similar to Earth’s seas. Consequently, lunar mapmakers of the time gave them names beginning with “mare,” the Latin word for sea, and those names persist to this day.

9) The Moon does not rotate. Many think that, because the same side of the Moon always faces the Earth, it doesn't spin. In fact, if it did not rotate on its axis, we'd eventually see all parts of the Moon parade by us over the course of its month-long orbit around Earth. But we don’t, do we?

Millions of years ago, the strong pull of Earth’s gravity put the brakes on the Moon’s spin, slowing it down until its rotation became synchronous with its orbital motion. Now the Moon makes one complete rotation on its axis in the same time it takes to complete one orbit around the Earth. You can picture this slow rotation best if you imagine observing the Earth/Moon system from the Sun. From your vantage point on the Sun, you could watch Moon circling Earth, turning just enough on its axis to keep the same face toward Earth as it went around. And from the Sun you’d notice that, over the course of a month, your view of the Moon’s surface continually changed until you'd seen it all, proving that it was rotating.

8) Dogs and wolves howl at the moon. This is a common belief--perpetuated in popular art, music, and film--but there's no scientific evidence that it is so. Dogs and wolves howl to communicate with one another. A couple theories as to why humans have imagined this causal relationship between the Moon and howling animals are: a) Animals, particularly predators, may be more active on moonlit nights when they can see better, and b) When we hear animals howl at night, we're more likely to notice a big moon in the sky if it’s plainly visible. However, we may not recall all the times we heard animals howl when there was a crescent moon or no moon in the sky. This is called selective memory, and we use it to perpetuate our already-held beliefs.

7) The Full Moon is larger when it’s near the horizon than when it’s overhead. This effect, known as the Moon illusion, has been recognized since antiquity. How many times have you seen the rising Full Moon hanging just above the eastern horizon and thought to yourself, “The Moon looks huge!”? In fact, the Moon is a little nearer to us and therefore slightly larger in apparent size when it’s high in the sky. Think about it: as the Earth spins east, we are brought toward the Moon.

So what causes us to believe otherwise? The second century mathematician and astronomer Ptolemy first postulated that foreground objects near the horizon, such as trees and buildings, give us something with which to compare the low Moon, making it seem larger. Modern scientific researchers call these distance cues. They are still considered in current theories about the Moon illusion, along with the physiology of our eye muscles and the neurological processes in our brains. Some believe evolutionary selections were made for useful human survival skills like seeing eye-level objects better than high-in-the-sky objects. This skill might improve the chances of finding shelter and food, as well as detecting danger. But there is still no one definitive answer as to why we experience this optical illusion.

6) The Moon has a “dark side.” The Moon has no side that is always dark. The entire surface of the Moon is illuminated by the Sun at one time or another during its month-long orbit around the Earth. However, only half of the Moon’s sphere can be illuminated by the Sun at any given time (shine a flashlight at a baseball, and you'll get the idea).

Although the Moon has no dark side, it does have a far side that always faces away from Earth. Because the Moon’s rotation (spin around its axis) is in lockstep with its revolution (orbit around the Earth), the same lunar hemisphere always faces us.

Stay tuned for next month’s Full Moon to find out which moon myths made my top ten list in the Numbers 5 through 1 slots. Until then, happy howling!