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General Lunacy

August 9, 2013

The Earth has the largest moon of the terrestrial planets of our Solar System. It's so large that we witness spectacular total eclipses of the Sun. There are no eclipses for Mercury or Venus, since they have no moons. Mars has two small moons, Phobos and Deimos.

Phobos does eclipse the Sun on Mars, but these are just annular eclipses in which the full disk of the Sun is not blocked. Although these happen twice each Martian day, they are of very short duration. Deimos is so small that when it passes between Mars and the Sun, it looks like a sunspot, and there's not that much reduction in solar intensity at the surface of Mars. It's more proper to say that Diemos transits the Sun rather than eclipses it.

2013 lunar transit observed by NASA's Solar Dynamics Observatory.

Lunar transit observed by NASA's Solar Dynamics Observatory on March 11, 2013, at 8:00 AM EDT.

Since the Solar Dynamics Observatory is in Earth orbit, this transit photograph is a good simulation of a most perfect solar eclipse.

(NASA/SDO image.)

The huge size of Earth's Moon is an anomaly. The leading theory of the origin of the Moon is that the Earth was impacted by a large body about 4.5 billion years ago, and the remaining debris reassembled into a smaller Earth and the Moon. This theory still has a few gaps, so there's still no scientific consensus on the matter.

No matter how the Moon came to be, we're fortunate that it's there, since it's possibly the reason why life exists on Earth. Charles Darwin's idea of the abiogenesis of life on Earth was that it started with a proper chemical soup in a "warm little pond."[1] The lunar tides are thought to have provided the means of concentrating ocean chemicals in littoral ponds.[2-4]

Because of its large size, the Moon has a present influence on terrestrial life because of its cycle of night time illumination over a period of the lunar month. There have been several studies showing lunar rhythms in aquatic animals.[5] A 1958 study showed evidence for lunar periodicity in the breeding of the scallop.[6]

At about the same time, it was found that the numbers of several species of flying insect, Ephemeroptera (Mayfly), Trichoptera (Caddis fly), and Diptera (true fly), caught in light traps showed periodic fluctuations that correlated with the phase of the Moon. The cause was attributed to a lunar rhythm of emergence.[7]

Closer to home, it's quite apparent that the period of the human menstrual cycle matches the lunar month. A 1980 study showed that for a sample of 312 women, the mean and median of the menstrual cycle was 29.5 days, or exactly a lunar month.[8] Not only that, but the cycles were found to be in phase with the lunar month. Thirty percent of women have a menstrual cycle within a day of 29.5 days, and these tend to ovulate in the dark phase of the lunar period.[8] A follow-up study in 1987 showed that that such women tend to menstruate when the moon is full with a reduced probability of the onset of menses after the full moon.[9]

All this evidence of the Moon's influence lends credence to the results of a study recently published in Current Biology by scientists at the University of Basel (Basel, Switzerland), the Swiss Federal Institute of Technology (Lausanne, Switzerland), and the Centre for Sleep Medicine, the Hirslanden Clinic (Zollikon, Switzerland). The study examined the popular conception that people sleep poorly around the time of the full moon.[10-13] The study overcomes deficiencies of past studies, which included biases, statistical weaknesses, or inconsistent methods.[13]

Woodcut by Vilhelm Pedersen

Shielding Mother from the Moon's Rays?

A woodcut by Thomas Vilhelm Pedersen (1820-1859). Pederson was the first artist to illustrate the tales of Hans Christian Andersen.

(Via Wikimedia Commons.)

The scientists studied thirty sleeping volunteers in two age groups in a laboratory setting. Each study subject slept for two separate nights under close observation, and they were not aware of the purpose of the study.[12] The scientists monitored electroencephalographic (EEG) activity during non-rapid-eye-movement (NREM) sleep, and the secretion of the hormones melatonin and cortisol.[10-12]

They found that at the time of the full moon, the EEG delta-wave activity during NREM sleep, which is an indicator of deep sleep, decreased by 30%. The time to fall asleep increased by five minutes, and the duration of sleep, as assessed by EEG, was reduced by twenty minutes.[10-13] These changes were associated with diminished endogenous melatonin levels,[10] and the study subjects assessed their own sleep as being poorer during the full moon.[11]

Biologist Christian Cajochen, the lead author of the study, is quoted in Science as saying, "A lot of people are going to say, 'Yeah, I knew this already. I never sleep well during a full moon.' But this is the first data that really confirms it... There had been numerous studies before, but many were very inconclusive."[13] Cajochen is further quited by BBC News as saying, "The lunar cycle seems to influence human sleep, even when one does not 'see' the Moon and is not aware of the actual moon phase."[12]

One of the most interesting aspects of the study is that it wasn't designed to detect lunar rhythms of sleep. The lunar correlation was done retrospectively using older sleep data.[12] These data were collected between 2000 and 2003, and the idea of looking for lunar rhythms was hatched by the scientists while visiting a pub during a full moon.[13] Neuroscientist, Kristin Tessmar-Raible of the Max F. Perutz Laboratories in Vienna, is quoted in Science as saying, "What's nicest about this study is that it uses data that wasn't originally intended for this purpose, so you know there couldn't be any bias and that makes it quite convincing."[13]

Another interesting aspect of the study is that the study subjects couldn't see the moon, so enhanced night time illumination is not the cause. It appears that this is a biological clock internal to humans, a relic of our ancestors, maintained through internal hormones.[13] The study data were not collected over a lunar month for any single study subject, which is something that might be tackled in follow-up experiments.[13]


  1. Alison Pearn, "Darwin's "warm little pond," The Darwin Project, February 15, 2012.
    "It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present.— But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts,—light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter wd be instantly devoured, or absorbed, which would not have been the case before living creatures were formed." (Letter to J. D. Hooker, February 1, 1871)
  2. Carlo Denis, "Archaean tides and the origin of life," National Museum for Natural History, Luxembourg (PDF File).
  3. Richard Lathe, "Fast tidal cycling and the origin of life," Icarus, vol. 168, no. 1 (March, 2004), pp. 18-22.
  4. Anil Ananthaswamy, "No Moon, no life on Earth, suggests theory," New Scientist, March 18, 2004.
  5. R. M. McDowall, "Lunar Rhythms in Aquatic Animals A General Review," Tuatara, vol. 17, no. 3 (December, 1969), pp. 133-143.
  6. James Mason, "A possible lunar periodicity in the breeding of the scallop, Pecten maximus (L.)," Journal of Natural History, ser. 13, vol. 1, no. 9 (1958), pp. 601-602.
  7. W. Danthanarayana, "Lunar Periodicity of Insect Flight and Migration," Proceedings in Life Sciences (1986), pp. 88-119.
  8. Winnifred B. Cutler, "Lunar and Menstrual Phase Locking," American Journal of Obstetrics and Gynecology, vol. 137 (1980), p. 834.
  9. Winnifred B. Cutle, Wolfgang M. Schleidt, Erika Freidmann, George Preti and Robert Stine, "Lunar Influences on the Reproductive Cycle in Women," Human Biology, vol. 59, no. 6 (December 1987).
  10. Christian Cajochen, Songül Altanay-Ekici, Mirjam Münch, Sylvia Frey, Vera Knoblauch and Anna Wirz-Justice, "Evidence that the Lunar Cycle Influences Human Sleep," Current Biology (Advanced Online Publication), July 25, 2013, DOI:10.1016/j.cub.2013.06.029.
  11. Doch kein Mythos: Schlechter Schlaf bei Vollmond, University of Basel Press Release in German, July 25, 2013; Bad sleep around full moon is no longer a myth, University of Basel Press Release in English, July 25, 2013.
  12. Michelle Roberts, "Full Moon 'disturbs a good night's sleep'," BBC News, July 25, 2013.
  13. Sarah C. P. Williams, "Yes, You Can Blame the Moon for a Bad Night's Sleep," Science. July 25, 2013.

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