Below is the full text, written by Dr. Jerry LaSala, of the script of the Momix/PCA Offstage special event, “A Journey to the Moon’s Lunar Seas.?
“I find that the surface of the Moon is not smooth, uniform, and precisely spherical as a great number of philosophers believe, but is uneven … not unlike the face of the Earth, relieved by chains of mountains and deep valleys … As for the large lunar spots, they are even and uniform and might very fitly represent water …? So wrote Galileo Galilei in 1610, reporting on his observations of the Moon with his newly-built telescope. The telescope had been invented the year before in Holland, and Galileo soon figured out how to make his own. He quickly used it to study the heavens and published a pamphlet called “The Starry Messenger? in 1610, describing the wonders he saw. The confirmation that the Moon was a world much like the Earth was an important step toward learning our true place in the Universe.
As we look at the beautiful full Moon, we see the pattern of dark and light areas that we call “The Man in the Moon.? Today we know there is no water on the Moon, but to Galileo and his contemporaries, the smooth, gray areas that cover much of the Moon’s face looked like water, so they called them “Seas? (maria in Latin). By the middle of the 17th Century the Jesuit astronomers Giambattista Riccioli and Francesco Grimaldi had mapped the Moon and given the maria the fanciful names we still use today: Mare Imbrium, the Sea of Rains; Sinus Iridium, the Bay of Rainbows; Mare Tranquilitatis, the Sea of Tranquility; Mare Serenitatis, the Sea of Serenity; and Oceanus Procellarum, the Ocean of Storms, to name a few.
Galileo was not the first to imagine Lunar Seas. As long ago as 500 BC, the Greek mathematician and philosopher Pythagoras and his followers asserted that the Moon was a world like the Earth, with oceans and mountains. From ancient times, the Moon has inspired us humans, leading us to produce great science, great music, great poetry, and great art.
Probably the most noticeable thing about the Moon, aside from its presence at all, is its changing shape, the so-called phases of the Moon. Sometimes we see the Full Moon – a perfect round disk in the sky, lighting our night. Other times we see only half a disk, what we call a quarter Moon; sometimes we see only a thin crescent, rising shortly before the Sun, or setting shortly after it. Watching these changes, we find that the Moon goes through a cycle of phases: from Full, it goes to a nearly-full phase called Gibbous, then the half-Moon lit on the left (Eastern) side that we call Last Quarter. A few days later we see the sliver of the Waning Crescent Moon rising a little before the Sun, and then the Moon disappears from view for a day or two in the phase we call New Moon, although “No Moon? might seem more appropriate. Then we find the Waxing Crescent setting shortly after sunset, followed by First Quarter, Waxing Gibbous, and back to Full Moon. The names of the phases start the cycle at New Moon, hence First Quarter and the Moon is growing and Last Quarter as it is returning toward New. Also, the words “waxing? and “waning? aren’t very common anymore except when we’re talking about the Moon’s phases, so it’s worth pointing out that “waxing? means “growing? and “waning? means “shrinking.? The whole cycle of phases, from one New Moon to the next (or one Full Moon to the next) takes 29 and ½ days. Our calendar month is an approximation of this period and in fact the word “month? comes from “Moon.?
So why does the Moon go through this cycle? Most people, when asked why the Moon changes shape, answer that it’s because of the Earth’s shadow falling on the Moon. But this can’t be right! You know, I’m sure, of two pieces of evidence that rule out the Earth’s shadow as the culprit. First of all, we all know the Earth is round – a globe. Now a ball always casts a round shadow, but look at the “shadow? here, at First Quarter Moon, and here, at Gibbous Moon; there’s no way a ball could cast that shadow! The other point is a little more subtle, but I’m sure you’ve all, at one time or another, noticed the Full Moon rising, and probably commented on how big and beautiful it looked. Now try to remember: where was the Sun when this was happening? Answer: it was just setting! So the Full Moon rises at sunset. But think about it: the Full Moon is rising in the East, the Sun is setting in the West, and we, on the Earth, right in the middle between the two. If there was ever a time that the Earth’s shadow would fall on the Moon, that would be it, but we see no shadow at all! So the Earth’s shadow doesn’t cause the Moon’s phases. What does?
In some sense, we might say it’s the Moon’s own shadow! Here’s what I mean. We have a pretty good idea of what the Moon is made of: rocks and dirt, or something like that. (We’ve even brought back some of these rocks!) And we know that rocks and dirt don’t glow! So the Moon only shines by reflecting the light of the Sun. And just as the Sun can only shine on half the Earth at a time, giving us night and day, so it can only illuminate half the moon at a time, so at any moment half the Moon is light and half dark. Now the Moon goes around the Earth, completing one orbit in about a month. As it does so, the angle between the Sun, Earth, and Moon changes, letting us see different amounts of the Moon’s lit side.
This diagram shows the Moon in its orbit around the Earth; the Sun is far away off to the right side, so only that side of the Moon is illuminated. When the Moon is here, we see that the whole lit face is toward the Earth, so we see it all: Full Moon. Notice that this occurs when the Earth is between the Moon and the Sun, so the Moon will appear opposite the Sun in the sky – rising as the Sun sets, just as we have observed!
When the Moon gets to this point in its orbit, we see half the lit side: a Last Quarter Moon; here we see only a tiny bit of the lighted side: this is the Waning Crescent. When the Moon gets to this position, between the Earth and the Sun, the illuminated face is turned completely away from us and we can’t see the Moon at all: New Moon. As the Moon continues around its orbit, it goes through a similar set of waxing phases as it returns to Full Moon in 29 ½ days.
For thousands of years people have used the phases of the Moon for timekeeping. We’ve also imagined that the Moon has other influences on our lives. Some other natural cycles take about a month, and many people imagine them to be related to the Moon; in addition, we’re very good at imagining patterns even where there aren’t any! So many people imagine that all kinds of human behavior is related to the phases of the Moon. They claim that there’s more crime at Full Moon, that most babies are born at Full Moon, that werewolves emerge at Full Moon, and especially that insanity is more pronounced at Full Moon. None of these claims is supported by real evidence, but people believe them anyway! The supposed link between the Moon and insanity is the source of our words “lunatic? and “lunacy.? In fact, the title of this show, and the Momix dance presentation inspired by it, comes from a play on those very words. We asked Moses Pendleton, the creator of “Lunar Sea,? how he chose the name and here’s what he said: “Well the piece went through many titles. I couldn’t decide and I finally said ‘This is sheer Lunar-cy,’ and so it was, and so it is.?
The Moon influences the seas of the Earth as well! We are all familiar with the tides – the rise and fall of the ocean’s level twice a day. People have recognized for thousands of years that the tides have something to do with the Moon: at low tide, the Moon is generally rising or setting, while at high tide the Moon is either high in the sky or not to be found. Isaac Newton figured out the Lunar connection with the tides in the 1600s. Newton had figured out that gravity gets weaker with distance, and that the Moon has gravity that pulls on the Earth and its oceans. Now the solid Earth and the watery oceans respond differently to the Moon’s gravitational tug. The Earth, being solid, acts as if the Moon’s gravity were pulling on the Earth’s center, but every drop of water in the oceans responds on its own. In particular, the ocean here, directly beneath the Moon, is about 4000 miles closer to the Moon than the center of the Earth, so the Moon’s gravity pulls harder on the water than on the solid Earth, and the water bulges upward. On the other side, the ocean is 4000 miles farther than the center of the Earth, so the Earth is , in effect “pulled out from under the water,? leaving another bulge on that side. To create these bulges, water has to flow from the other parts of the oceans, leaving two shallow areas here and here. The bulges are, of course, the areas of high tide, and the shallow spots are low tide. As the Earth rotates each day, we are brought from high tide to low and back to high again twice a day.
Some biologists believe that Moon played a part in the evolution of life as we know it on the Earth, that without the Moon to stabilize the Earth’s rotation and provide large tides, life, if it existed here at all, would be very different from what we are familiar with. Whether that’s true or not I don’t know, but it’s surely true that the Moon played an important role in our scientific evolution.
Everyone knows the story of Newton and the apple – back in 1666 or so, Isaac Newton was sitting under an apple tree when an apple fell and hit him on the head and aha! He discovered gravity! Well, there must be something bogus about that story! After all, it wasn’t news that apples fell out of trees, even in the 17th century. No, Newton was actually trying to solve the problem of the Moon and why it goes around the Earth. Newton’s experiments with Earth-bound objects convinced him that the Moon should fly off in a straight line if there weren’t a force pulling it toward the Earth. Similarly, the planets must be pulled toward the Sun or they would leave their orbits and fly off forever. But what was this cosmic force holding the Moon and planets in place? That’s the problem Newton was working on when he saw the apple fall (he never actually said it hit him on the head). Newton realized that the apple fell because a force pulled it toward the Earth; the Moon doesn’t fly off because a force pulls it toward the Earth. Perhaps, Newton thought, the two forces are really the same force: Gravity!
Well that’s a great idea, but is it correct? That was Newton’s next problem, to try to show that the force of gravity was the same force holding the Moon in place. Here’s how he did it. In the early 1600s, Johannes Kepler had worked out the laws that describe the motion of the planets around the Sun; up until then most people believed the Sun and planets circled the Earth. Kepler found that planets farther from the Sun, like Saturn, move more slowly than those closer to the Sun, like Venus, and his so called Third Law allowed him to calculate how much more slowly. New ton was able to use this information to figure out how the force keeping the planets in orbit decreased with distance from the Sun. Now he had something to go on.
Newton knew how strong gravity is here on the Earth’s surface – he could weigh the apple! He knew how strong the cosmic force holding the Moon in orbit had to be. Assuming gravity decreased with distance the same way the force on the planets does, he could calculate how strong gravity would be at the distance to the Moon. As you can probably guess, he found that the strength of gravity was just what was needed to keep the Moon in orbit! In other words, we don’t need a special cosmic force to keep the planets in place: good old gravity does the job!
So the Moon was very important to the discovery of Newton’s Law of Gravitation. One part of that law says that all objects have gravity, and another part allows us to calculate how strong any objects gravity is. So despite what anyone might have told you, the Moon has gravity, but when we calculate its strength, we find that gravity on the Moon is only one-sixth as strong as on Earth. That means that if you weigh 120 pounds here on Earth, you’d only weigh 20 pounds on the Moon. That’s quite a weight-loss plan! It also means that everything falls six times more slowly on the Moon. This video shows Apollo 15 Commander David Scott dropping a hammer and a feather on the Moon. Since the Moon has no air resistance, they both fall at the same rate, but especially note how much more slowly they fall than if the hammer had been dropped here on Earth.
This next video shows astronaut Alan Shepard walking along the Moon’s surface. Notice how he seems to bounce high and come down slowly. Again, that’s due to the Moon’s low gravity. This low gravity inspired Momix choreographer Moses Pendleton to imagine dancing on the Moon, where dancers could jump high and come down slowly (they couldn’t breathe, of course, but they could sure jump!), and he decided to create effects that would make Earth-bound dancers appear to float like their Lunar counterparts.
Here we can see a little of that choreographic magic. [Use Moon Panorama, PCA Momix video on laptop] We asked Moses Pendleton how he did it, and he told us: “Well actually the subtitle for this Lunar Sea was ‘No Visible Means of Support.’ Half of the dancers are invisible, the ones who are in fact porting the ones who are visible about so that they seem to float and fly and swim and move in a fantastic way. It creates the mystery of the piece.? Then we asked him how we audience members ought to prepare ourselves for the performance, and he said: “I would say, sit back and let the Moon come to you. Don’t try to think too much or anticipate anything or expect anything other than the unexpected when you come to see Lunar Sea.?
