Now that the Supermoon hoopla has died down, it’s time to reflect on its meaning and significance. On a factual level, the full moon was indeed as close as it will get until 2034. On the level of human experience, the elevation of the event to “super” status was utter malarkey. However, it was malarkey with a purpose.
First, some background. The phases of the moon happen because the moon orbits the Earth every 27.3 days — once a “moonth.” (Hey, where do you think the word “month” comes from?)
Lunar phases are the result of the angle from which the sun is shining on the moon from our vantage point. On a full moon night, the sun is behind Earth, and the moon is in front of it. The full face of the moon is illuminated, so we see a full moon.
However, the moon’s orbit is not a perfect circle. Instead, the circle is stretched out into an oval shape called an ellipse. As a result, during every 27-day lunar orbit, the moon gets as close as 225,623 miles to the Earth, a condition called perigee. Fourteen days later, it gets as far as 252,088 miles from the Earth, a condition called apogee.
That sounds like a lot, but the change happens quite gradually from full moon to full moon. Next month’s full moon won’t look much different. Neither will the full moon after that.
A Supermoon, when the full moon and the closest approach coincide, happens only about once a year. Months will pass before you see a Micromoon, when the moon is full and at its farthest point.
Why are the events so separated in time? The lunar phases don’t match up with the moon’s orbit. As the moon is orbiting Earth, our planet is also orbiting the sun. Thus, the angle of the sunlight hitting Earth changes from day to day. Recall that the moon orbits Earth every 27.3 days. In the meantime, Earth is traveling around the sun, which changes the sun’s angle slightly. Thus, it takes about two extra days, 29.5 of them to be precise, for the moon to go through a full set of phases.
In fact, the difference in size between a Supermoon and Micromoon is only 14 percent. I have never been able to notice the difference. You might – if you have a distinct memory of what the full moon looks like at apogee and perigee even though months separate the two experiences.
Here’s the trick the marketers of such events don’t generally tell you: The moon always looks bigger when it is rising. The phenomenon is called the moon illusion. When you observe it close to the horizon, you unconsciously compare its size to foreground objects like trees and buildings. A few hours later, when the moon has risen higher and is on its own in the sky, you have nothing to compare it with, and it looks smaller. That’s the reason the press-release gang always tells you to go out at sunset and observe the rising moon on Supermoon nights.
So why all the Supermoon hoopla? The writers of press releases, notably from NASA, sincerely want you to be fascinated with the universe and everything in it. They figure that if they can just get you outside, the rest will follow.
It’s easy for someone like me, a soldier on the front line of such efforts, to love such gentle trickery. But I don’t because it raises expectations out of all proportion to the quality of the experience. An event that is equally beautiful every month is now marketed as the most spectacular until 2034.
Such nonsense leaves folks like me facing a lot of public disappointment afterward. Those folks at NASA should try telling rooms packed with people that the tiny (but beautiful) image of Mars in a large telescope is all they get when they were expecting Mars to look “as big as the full moon.” Better yet, they should try explaining it to that 12-year-old kid who was totally stoked by the hype and then utterly disappointed because of her unfulfilled expectations.
And thus I say, forget about that Supermoon silliness. Go out and watch the next full moon rise — as I did one fine night when I was about 15.
I stood outside just after sunset as the moon rose above a neighbor’s house. As it slowly appeared, first as a tiny burst of light and then as a larger and larger lunar lump until the whole disc was exposed, I remembered something I had read somewhere in a book.
The moon was not rising. Like everything in the sky, the moon only appeared to move. Its “rising” was Earth spinning in the other direction. At that moment, the moon became a fixed point, and everything around me – the houses, the trees, the grass beneath my feet, and, in fact, me — was rotating in the opposite direction at 680 miles per hour.
For an instant, I stood on a spinning ball hurtling through space. I dropped to one knee in one of those glorious swoons that happen when what is in your head is abruptly and miraculously transported to your heart.
And this I swear, gentle reader. Every one of thousands of talks I have given on astronomy, every plea for donations to Perkins Observatory, every word I have written on stargazing for the past 30 years, every time I have pointed a telescope for some third grader, and every time I have begged people to look up at the sky have their origin in that magical moment.
Any night is a good night to go out and watch the moon rise or stare with wonder at a sky filled with stars. So go out and do it. While you’re at it, take a child or three along with you and whisper softly about the wonder and majesty of the universe they live in. Who knows what might happen?
Tom Burns is director of the Perkins Observatory in Delaware.