Essays: Supermoon

Saturday, July 12, 2014

Supermoon

Supermoons occur tonight July 12^th, and again on August 10^th and September 10^th of 2014.

Show Don't Tell

Oft quoted writing advice from Anton Chekhov to his brother has been paraphrased as:

“Don't tell me the moon is shining; show me the glint of light on broken glass.”

Chekhov advised his brother, an aspiring writer, to "show, don't tell" which has become a guiding principle of writing. Show don't tell might be extended to scientific phenomena like the supermoon.

Elliptical Orbit

The moon orbits the earth in an elliptical path. Unlike a hypothetical circular path where the moon would always be equidistant from the earth, the moon's elliptical path means the distance between the earth and the moon varies over an orbital cycle.

The supermoon, or a full moon at perigee, is a phenomenon that occurs when the moon's orbital path transports it to its closest point to the Earth. The terms perigee and apogee describe the shortest and longest distance between the earth and the moon.

Full Moon at Perigee

A full moon at perigee would, by comparison, appear about 12-14% larger than the full moon at apogee because it is closer. If you held a ball at arm's length then brought it to your nose, the same ball would appear larger. Similarly, the full moon at perigee might appear larger, but only if we have a reference to compare it to ― like side-by-side images of full moons at perigee and apogee.

It's not what you look at that matters, it's what you see.
― Henry David Thoreau

Apparent Size Difference by Observers of the Full Moon at Perigee and Apogee

Super Moons and Natural Disasters

The moon has less gravitational pull when it is at apogee (farthest from earth) than when it is at perigee (closest to earth). The gravitational pull of the moon influences tides. The stronger gravitational pull of a moon at perigee leads to higher variation in the high and low tide levels.

Despite these gravitational variations, science hasn't established a definitive correlation between a full moon at perigee and its attendant gravitational pull, and the occurrence of natural disasters like earthquakes, floods, and volcanic eruptions.

"I think you'd be hard pressed to see a difference in tectonic activity during different lunar phases."
― William Burton, USGS Research Geologist

Lunar phases seem to have no discernible influence on seismic activity, weather patterns, or volcanic activity.

"This idea of blaming natural disasters on the phases of the moon goes way back to the Greeks. It has been around for hundreds and hundreds of years."
― Malcom Johnston, USGS Scientist Emeritus