Moon Madness

The Moon is our nearest neighbor in space and before electric lighting took over the night, it was humanity’s companion. Yet there is still quite a lot of popular misunderstanding about the Moon.

1. Didn't people used to think the Moon was made of green cheese – how silly, it’s not even green.

In the 16th century green cheese was cheese that hadn’t matured. It was rather moonlike, being circular, mottled and a creamy color, though it's not likely that anyone really thought the Moon was cheesy. But it would have made for a dig about someone’s gullibility. Today instead of expressing doubt with “Yeah, right,” you could say “Uh huh, and the Moon is made of green cheese.”

2. The “dark side of the Moon” never gets any sunlight.

The “dark side” of the Moon is the side that is never seen from Earth, dark meaning unknown. More usefully, it’s called the "far side". As the Moon orbits, all parts of it get sunlight, but we still see just one side. Probes have studied it, but the only humans who’ve seen the far side are Apollo astronauts.

3. The same side of the Moon always faces us because the Moon doesn’t turn on its axis.

It’s just the opposite. The only way the same side can always face us is that the Moon rotates once in the time it takes to orbit Earth once, as shown in this diagram.

4. The phases of the Moon are caused by the Earth’s shadow.

The Moon isn’t in our shadow except during a lunar eclipse. It seems to change shape because as it orbits, the angle between us and the Moon and the sun changes to give different views of the illuminated half of the Moon. It’s shown in this diagram.

5. Since the Moon is rarely blue, “once in a Blue Moon” refers to a rare event.

Sometimes atmospheric dust makes the moon look blue, but a “Blue Moon” isn’t usually literally blue. It can be the second of two full moons in the same month. This idea grew from a misreading of a traditional almanac which explained that a Blue Moon was the third full moon in a season that had four of them. Twelve full moons had names which related them to months or seasons, so a separate name for any extra moon kept these relationships. Yet however you define a Blue Moon, it is indeed a rare event.

6. There is no gravity on the Moon.

If there were no gravity, there would be no Moon. Gravity is what holds heavenly bodies together. However gravity on the Moon is about one-sixth that on Earth. So the Apollo astronauts – even with heavy space suits – were able to jump and skip, but they didn’t float off.

7. There is more lunacy when the Moon is full.

The so-called lunar effect is well-known and medical staff and police attest to it. Nonetheless it doesn’t exist. An analysis of studies looking at a variety of behaviors – including crimes, psychiatric problems and suicides – didn’t find anything related to the moon phase. Psychologists say that when we “know” something is true, we match what we see to what we expect. So people particularly notice certain events when the Moon is full without remarking on them at other times.

8. The Moon affects us because we are mostly water and the Moon’s gravity causes tides.

Gravity itself doesn’t cause tides. However the force of the Moon’s gravity on the near side of Earth is greater than on the far side. It’s the difference between these forces that causes ocean tides, so it works on a large scale. The difference between the Moon’s force on your head and that on your feet is effectively zero. Not so, if you were diving into a black hole. The force on your head would be much bigger than that on your feet and you’d be stretched out like spaghetti.

9. When there is a supermoon the increased gravitational pull of the Moon triggers earthquakes, volcanic activity, extreme tides and severe weather.

The term “supermoon” was invented by someone with more imagination than understanding. The Moon’s orbit isn’t circular and a so-called supermoon is just a full moon at perigee, i.e., at its closest to Earth. The last time this occurred was on March 19, 2011. The number of earthquakes at or above 5 on the Richter scale for the week around that date was about average. There were no volcanic eruptions, unusual tides or severe weather events.

10. Apollo 11 didn’t go to the Moon – it was all faked on a movie set.

There are claims that it was a hoax, but a notable lack of evidence. Dr. Phil Plait and others have looked extensively at these claims – there is a link in the References if you would like more information. I will merely note that this was at the height of the Cold War. I could more easily believe that the Moon is made of green cheese than imagine getting a fake moon landing past the Russians.

References:

(1) Deborah Byrd, “When Is the Next Full Moon?” http://earthsky.org/astronomy-essentials/when-is-the-next-blue-moon
(1) Scott O. Lilienfeld & Hal Arkowitz, “Lunacy and the Full Moon,” Scientific American http://www.scientificamerican.com/article.cfm?id=lunacy-and-the-full-moon
(2) Phil Plait, “Yes, We Really Did Go to the Moon!”
(3) “Earthquake Facts and Statistics,” United States Geological Survey, http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php and “Latest Earthquakes in the World – Past 7 days,” http://earthquake.usgs.gov/earthquakes/recenteqsww/ (accessed 2011-03-23 00.18 UTC)