Moon Showers

By Bob Berman|Tuesday, August 01, 1995
With a brilliant full moon ruining this month’s Perseid meteor shower, it’s tempting to make our natural satellite a scapegoat for other problems as well, as people have through the ages. The full moon, of course, does not foster mental illness--psychiatric hospital admissions show no rise. There’s no link to crime either, at least not according to a study in Dade County, Florida. And there are no more births nine months after the full moon than after any other phase. Even so, attributing surprising powers to the moon is not as misbegotten an idea as it sounds. Recent studies have turned up some cor-relations that are almost as unexpected and odd as any found in folklore.

Even before Isaac Newton explained the phenomenon, people had noticed the synchroneity of lunar phases with the rise and fall of the ocean tides. More recently the moon has been found to deform--by several inches--Earth’s solid crust. Less well known is the moon’s ability to generate an atmospheric tide, a gaseous pulse that creates daily changes in air pressure. This air tide may somehow be linked to the striking but unexplained coincidence of lunar phases with cloudiness, rainfall, and even hurricane formation.

In short, the moon seems to have an uncanny influence on the weather.

Earlier this year researchers at the University of Arizona who were analyzing satellite data announced yet another effect: at the time of full moon, the temperature of the lower four miles of Earth’s atmosphere increases by a few hundredths of a degree. It’s not enough to allow you to leave your sweater home on moonlit nights, but it’s more than enough to show that Earth’s climate is even more complex than scientists had thought.

The moon, they suggest, raises the temperature of our atmosphere in two ways. First, the moon’s surface, warmed by the sun, radiates thermal energy at us like an electric bathroom heater. This energy is some 100,000 times less intense than the heat we receive directly from the sun, but it’s probably supplemented by a second mechanism: the full moon’s simple mirroring of sunlight at the nightside of Earth.

The mirror effect is slight because the moon is one of the least shiny objects in the known universe. Its albedo of 10 (which means it reflects just 10 percent of the sunlight that strikes it) exactly matches the reflectivity of asphalt. The moon’s appearance, then, is no brighter than if its surface were entirely paved, like an enormous mall. This helps explain why, romance aside, the full moon drearily appears a half million times less bright than the sun.

Other investigators think the moon’s influence involves even subtler mechanisms. Some suggest that the statistical increase in thunderstorm activity observed around the time of the full moon may be caused by our planet’s magnetic field undergoing moon-induced distortions, which might then somehow affect the electrical properties of the atmosphere. Other researchers studying the lunar-phase connection suggest that rainfall might even increase when clouds are seeded by meteoritic dust pulled into Earth’s orbit by the moon.

So the moon can’t win this month. If skies are clear, the full moon washes out the summer meteors, the year’s best celestial show. If it’s cloudy, then it’s not meteor showers but rain showers that we can blame on Earth’s nearest neighbor. It’s enough to make you go out and howl at the moon.
Comment on this article