Imagine my fourth-grade classroom. A shelf of math books and stacks of Weekly Readers. The smell of cedar shavings and nose-wrinkling disinfectant. Pale green walls covered with maps of Marco Polo’s travels along the Silk Road. Two high windows looking out across the East River at the foreign kingdom of Queens. A dark December day outside but inside, on Miss Allison’s desk, the Sun is shining. The Sun, a 40-watt light bulb mounted on a wooden platform, shines on a pink rubber ball, which casts its shadow on a ping pong ball, all of it simulating an eclipse of the Moon.
This is the year of Marco Polo. In one corner of the classroom we’ve built a ship and in it we sail to China, though we call it Cathay. We meet Kublai Khan and learn how to pronounce “Xanadu” and how to use an abacus. Our favorite book is The Travels of Marco Polo, though we call it by its original name, Book of the Marvels of the World. We are 9 years old, and the world holds marvels aplenty, and if they can be catalogued and contained between the covers of a book, we are nothing but curious.
It is also the year of John Glenn’s 4-hour, 55-minute journey into space, orbiting the earth three times, an event that has threatened to upstage the entire Polo expedition and relegate Khan to a position of minor bureaucrat. As far as we’re concerned, space is the new Xanadu. On Feb. 20, 1962, I record the following:
Colonel John Glenn has been in America’s first orbital flight for one hour twenty minutes as of 11:15 a.m. this twentieth day of February in the year of Our Lord, 1962. He is now approaching the Pacific coast of North America. His speed is five miles per second. He is now over Cape Canaveral. The first orbit has taken eighty-nine minutes! Glenn’s flight today is a great step in the future attempt to land two men on the Moon at the end of this decade.
We are thrilled with this benchmark, this development that seems to have taken place right above our heads. Because isn’t that where space is? What is space anyway? And as for the Moon, suddenly we have a hundred questions. Do we see only one side of it? Why does it change size and shape? Is there winter there? Gravity? What time is it on the Moon? What’s it made of? How did it get there? Why do we want to go there? What if the Russians get there first?
When it comes to questions, Miss Allison is no rookie. She knows exactly what’s needed: a light bulb, a rubber ball and a ping pong ball. We gather around her desk. She flips a switch and the light bulb fires up. We ooh and aah. It’s only a light bulb, but in a willing suspension of disbelief we’re sure it’s the birth of the Sun. She maneuvers the rubber ball of Earth and sets us whirling around the Sun, our local star, explaining it will take a year. And because planet Earth tilts a little, we have winter now in the northern hemisphere while Australia has summer. Tilting is a surprise to us—a surprise and a worry. It implies instability, a wobbling we can suddenly feel underfoot. But the intrepid Miss Allison continues, reminding us that as the rubber ball circumnavigates the Sun it also spins on its axis, creating our 24-hour day. 365 of these spins—366 in a leap year—and we’ll be back where we started.
“But the Moon?” we say. “Bring on the Moon!”
Miss Allison sends the ping pong ball into orbit around our red rubber Earth. She shows us how it moves around us, taking its time, about 28 days, while all the while we’re spinning, one full turn a day. The position of the orbiting Moon in relationship to the Sun is what creates the Moon’s different phases. If the Moon rides between Earth and Sun, the side we see from Earth is all in shadow. We call that a new moon. Halfway through the Moon’s 28-day orbit the Earth lies between Moon and Sun (though most of the time on a different plane which is why the Earth’s shadow only occasionally falls across the Moon causing a lunar eclipse), and the face of the Moon we see from Earth is fully illuminated. We call that a full moon. Crescent moons, quarter moons (erroneously called half-moons), gibbous moons, waxing and waning moons—these are all stages in between the new and the full, and all determined by the position of the Moon in relationship to the Sun.
Tricky, isn’t it? Yet so much easier to understand if you can see it; that is, if you have Miss Allison’s ball-and-light bulb contraption. We can see why the Moon rises almost an hour later each day: It’s a chasing game, a game of tag. In its month-long orbit of the Earth, the Moon travels a little farther one day to the next, so from the same place on the rotating Earth it takes a little longer to catch up with it. This gives the appearance of moonrise on a 50-minute delay, but as we all know (and here Miss Allison sighs ominously), the Moon doesn’t really rise.
What!
There’s an uneasy shifting of bodies around our teacher’s desk, and swift on the heels of Copernicus she breaks the news: The apparent rising and setting of the Moon, like the apparent rising and setting of the Sun, is actually due to the turning of Earth rather than the movement of those two celestial bodies. The Sun isn’t fixed in space, but it doesn’t move around us. It orbits the center of our Milky Way Galaxy every 230 million years. The Moon moves around us, but much more slowly than we spin. It’s our spin that gives us the sense of Sun and Moon rising and setting. We aren’t the center of the universe, after all, not even the center of our solar system.
Our inquiry stumbles to a halt because the recess bell rings and as hungry as we are for knowledge, we are hungrier for graham crackers and chocolate milk. Miss Allison shoos us out the door with our snacks and coats. As we leave, she moves to her desk, so recently the launching pad for scientific discovery, and unceremoniously flips the switch and turns off the Sun.
