If you caught the full moon on Friday, you or a friend may have stories of how the moon affects us, biologically or behaviourally.
Some nurses will say emergency departments are busier, police officers will gear up for a busy night, and pub bouncers may complain about rowdy patrons.
Does the full moon affect humans and life on Earth? The answer, like many things, is complicated.
Firstly, this belief is not new - it has been around from millennia. "Lunacy" comes from the Latin word meaning "moonstruck".
There have been countless studies on whether the moon has an effect on humans - and the evidence is not strong.
Studies looking at menstrual cycles and the lunar cycles showed nothing convincing. Mental health problems have been looked at as well. Some studies have even looked at whether there are more motorcycle accidents on a full moon or supermoon.
With so much anecdotal evidence though, what is going on?
There is the classic image of a coyote howling at the moon or maybe the dog down the street seems to bark more. They probably are barking more as they can see more.
A full moon adds a substantial amount of light to the sky compared to when it is a new moon. The moon can add about 0.3 lux - luminous flux units per area. Your standard LED bulb in your bedroom or living room lights up the room between 1 and 10 lux.
With this extra light, animals like coyote and dogs, can see more and therefore will likely howl or bark at more objects they see moving - objects they would normally miss if the moon wasn't out. Just like animals, we can see more on a full moon night.
Around Mount Stromlo, where we keep it dark on purpose, I can walk around outside on a full moon.
This does support the idea that people are more likely to be active on a full moon night - as you can see more. Crime, going out, accidents, and other human activity is likely to increase.
However, there is also observational bias.
We notice things happen during a full moon because we notice the full moon more than other phases.
What happens when you buy a new car? You see that car, the model, or colour - everywhere. Does everyone have one now? No, you just notice it more because you are looking for it. We notice the full moon as it is bright, and nice to look at.
The full moon also always rises around sunset. We are likely to be out - driving home from work, going to dinner, or walking the dog. It is also rising at the horizon where it is in your line-of-sight. Do you notice the moon when it is three-quarters full and high above you? Probably not.
If the moon really did affect humans besides being able to see more, you would see an effect increasing towards the full moon.
The moon before or after a full moon should have an impact like the full moon, just slightly less. At a half moon, we should see about half the effect. In nearly all of these studies though, people don't.
So, while you notice and enjoy the full moon, don't forget, it is always there to look at.
- Brad E. Tucker is an Astrophysicist and Cosmologist at Mt Stromlo Observatory and the National Centre for the Public Awareness of Science at the ANU.
