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When you’re having a particularly weird night
and strangers are acting stranger than normal,
you’ve probably heard someone say,
“Must be a full moon!”
But here’s the thing:
The idea that the moon makes people behave strangely
is all a myth.
There are no more crimes, deaths,
or injuries when the moon is full.
But! That doesn’t mean that the moon
has no influence on our lives —
or the lives of other animals.
So, today, we’re going to look at
8 truths and myths about how the moon
affects things on Earth—
and separate the fact from the fiction.
If you’ve ever had trouble falling asleep
as the light of the full moon beams through your window,
you’re not alone.
Multiple studies have shown that people
sleep worse during the full moon.
And yeah, it might seem obvious
that it’s harder to fall asleep with a cosmic flashlight
shining in your window.
But studies show that the light itself
isn’t the only thing messing with your sleep.
One 2013 study monitored 33 volunteers
as they slept in labs that sealed out any moonlight.
On nights when the moon was full,
the volunteers took 5 more minutes to fall asleep
and slept for 20 fewer minutes overall.
They also had 30% less REM sleep,
which means they didn’t sleep as deeply.
In 2014, a similar sleep study found
similar effects in more than 300 patients.
Since the participants weren’t exposed to moonlight,
the researchers don’t think that was the variable here.
Also, if it were that easy to throw off sleep
with a little extra light, light pollution
would disrupt our sleep much more than it does.
Instead, many scientists think humans
may have a circalunar rhythm.
Just like circadian rhythms that work on a daily cycle,
circalunar rhythms work on the moon’s cycle.
Some other animals synch their behavior to the moon
—possibly because it makes it easier
for them to mate or find food—
so it’s not out of the question that humans
could have circalunar rhythms left over
from our evolutionary past.
Now a number of animals, like migratory birds,
frogs, and mollusks, use the Earth’s magnetic field
to orient themselves or navigate.
This ability is called magnetoreception.
And one especially cool example
happens in nudibranchs.
These are colorful, ostentatious sea slugs,
and they’re known to line up their bodies
with the Earth’s magnetic field.
But they also change that orientation
over the lunar cycle.
Scientists think that may be because
the moon's phase and position influence
the Earth's magnetic field.
See, every time the moon is full,
it passes into the Earth's geomagnetic tail.
That’s the piece of Earth’s magnetic field
that stretches out behind our planet,
thanks to a stream of high-energy particles
blowing in from the sun.
When the moon crosses into this region,
charged particles from the tail land on the moon’s surface
and temporarily give it a negative charge.
That negative charge then accelerates other ions in the tail,
creating a subtle shift in the magnetic field
that’s felt on the surface of the Earth.
The effect is super-small, so it’s not something
that would affect us at all, and very few people
have looked into it.
But one study suggests that all this geomagnetic activity
high above the Earth may lead these tiny, colorful mollusks
deep beneath the ocean to shift
their little bodies in a new direction.
Australia’s Great Barrier Reef is made
of tiny animals called coral polyps that extend
for two thousand kilometers off the coast.
These tiny organisms are generally pretty tame…
except once a year when it’s time to reproduce.
That’s when they have what locals call
the “annual sex festival.”
What! That’s what the locals call it!
I’m not making this up!
Once every year, the corals release their eggs and sperm
into the water all at once, in what looks like
(I kid you not)
a colorful, underwater snowstorm.
But as weird as it sounds
(and it sounds pretty weird)
it happens for a good reason.
Synchronizing like this gives them
the greatest chances of fertilization.
So they only do it when the timing is exactly right
— when the tides, salinity, water temperature,
and daytime length hit the perfect levels.
But most important of all:
It always happens a few days after a full moon.
Corals know when the moon is full
thanks to photoreceptors that can sense changes
in the blue wavelengths of moonlight.
And the right amount of moonlight
is the last piece of information they need to know it’s time.
So when that light is just right?
It’s spawning time.
You probably know that the moon
influences the ocean’s tide.
But maybe you didn’t know that the moon
also creates tides in our atmosphere.
Ocean tides happen because the moon’s gravity
creates two bulges in the ocean:
one right beneath it, and one on the same spot
on the opposite side of the planet.
But it also does the same thing
to our atmosphere.
As the moon pulls the atmosphere towards it,
more air gets squeezed into a tighter space,
which puts the air in the bulge under higher pressure.
That higher-pressure air warms up,
and since warmer air can hold more moisture,
clouds don’t condense into rain as easily.
That difference is small, but it is measurable.
A 2016 study analyzed fifteen years of data
from the Tropical Rainfall Measuring Mission
and found a small decrease in rain in places
where the moon was directly overhead.
The idea that menstruation is tied to the lunar cycle
is so ancient that it’s embedded in the word itself:
“menses” and “moon” both come from the Latin word for “month.”
And at first, that kind of makes sense.
After all, the two cycles are almost exactly the same length:
The lunar cycle lasts twenty-nine-and-a-half days,
and the global average menstrual cycle lasts twenty-nine days.
But while it may seem natural that the two cycles are linked,
research actually hasn’t found any connection.
Recently, scientists used the period-tracking app Clue
to analyze data from 1.5 million users,
and they found no correlation between
7.5 million menstrual cycles and the lunar cycle.
Well, then why are the two cycles so similar?
Well, there’s really no clear explanation.
Your intuition might suggest it’s a leftover
from early humans who needed to synchronize
with the moon… for some reason.
But if that were true, you’d think that the same thing
might show up in our closest primate relatives,
like chimpanzees, and that’s not the case.
Chimps’ menstrual cycle is a whopping 37 days.
So, in the end, the similarity may just be a coincidence.
One of the weirdest and coolest things
about scorpions is that they glow in UV light.
Flash them with an ultraviolet lamp,
and they will start glowing like your shoelaces
under a blacklight!
They do the same thing under UV light from the moon.
But for a long time, scientists didn’t know why.
To find out what was going on,
researchers in a 2010 study exposed a group
of scorpions to UV light until they couldn’t glow anymore,
and left a control group of scorpions alone.
Then, they exposed both groups to UV light.
The scorpions that couldn’t glow walked around aimlessly,
while those that could found somewhere to hide.
The thing is, scorpions’ eyes can’t actually
detect UV light very well, but somehow
they’re perfectly capable of avoiding it anyway.
The researchers now think that scorpions,
which are especially sensitive to green light,
detect their own green glow as a proxy for how much
UV light is coming from the moon.
So, they essentially use their bodies
as photon collectors for UV light, and
their bodies signal to them how much UV light is out there.
Researchers aren’t sure why scorpions seem
to use UV light rather than regular light for this,
but some have hypothesized that there’s some information
in UV that’s missing from visible light.
Whatever the reason, the glow from their bodies
helps them decide whether it’s a good night
to go out and forage for food
or hole up in a burrow to avoid predators.
The more they glow, the more UV there is,
and the more important it is for them to find shelter.
The belief that seizures can be triggered
by the full moon has been around for a long time.
It’s turned up in a range of cultures and time periods,
including indigenous communities in Bolivia,
Bantu populations in East Africa,
and ancient Greece.
But the belief doesn’t appear to hold water
— at least, not in the way people think it does.
In a 2004 study, scientists analyzed data
from an epilepsy monitoring unit.
They looked at around 700 seizures
of various types and found no significant clustering
around the full moon.
But when they looked at only epileptic seizures,
they found something surprising.
The number of epileptic seizures was actually lowest
during the full moon and highest during the last quarter.
So the full moon doesn’t trigger seizures,
but epileptic seizures do somehow seem
to be linked to lunar cycles.
A follow-up study in 2008 hypothesized that
the connection had to do with the amount of light
at night rather than with the actual phase of the moon.
They compared the frequency of seizures to the brightness
of each night, taking into account both the phase of the moon
and the amount of cloud cover.
And they found that epileptic seizures
were more likely to happen on darker nights.
The authors of the study suggested that these findings
could imply that the spike in seizures has
something to do with levels of melatonin,
which our bodies produce in higher quantities when it’s dark.
Dung beetles are hardworking insects that devote
a lot of time to one single-minded passion:
rolling feces into little balls to eat later on.
There’s a lot of competition out there for these dung balls,
so once a beetle is done rolling, it runs away with its treasure.
The safest route away from any would-be dung thieves
is a straight line, so that’s its preferred path.
At sunset, when dung beetles start to forage,
they use clues in the sunlight to orient themselves
in arrow-straight lines.
And they can do this because when sunlight
hits the atmosphere, a lot of it gets absorbed
and reemitted as polarized light,
in which all its waves vibrate in the same direction.
Dung beetles can detect and follow this polarization pattern.
Now that in itself isn’t actually that special.
Many animals do this with sunlight.
But the dung beetle is the first animal known to use
the much, much dimmer polarization of moonlight to do this.
Studies have found that even when the moon
is as small as a crescent, dung beetles can sense
the moonlight’s polarization and map a straight-line route.
But they do their best work during a full moon,
when the moonlight is bright and the polarization is strong.
The moon has some fascinating connections to us,
our environment, and our planet.
While you can’t believe everything you hear
about the power of the moon, the reality is often wilder,
weirder, and harder to believe than the fiction.
Thank you for watching this episode of SciShow!
And thanks to our Patreon supporters, who make it possible
for us to make episodes like this.
We’re always trying to separate the fact from the fiction
and highlight incredible things about our world.
And if you want to help make that possible,
join us at patreon.com/SciShow.
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