So in a setting I'm developing, a moon orbits a gas giant once every four days. It naturally is tidally locked to the parent body. Halfway through the day part of the cycle there is a two hour solar eclipse. If you assume hour zero is dawn, then the schedule looks somewhat like this for the part of the moon facing the gas giant (the part of the moon not facing the gas giant looks the same except it lacks the eclipse):

  • 0-22.9: daylight
  • 23-24.9: eclipse
  • 25-47.9: daylight
  • 48-95.9: night

Oh and I didn't specify it yet, but this moon is pretty Earth-like. Humans can easily survive on it; the gravity, atmosphere and temperature range is very similar.

A broad question anyone here can answer is: How would humans react to being placed on this moon?

However I'm looking for the answer to this question specifically: how would the day timetable specified above affect human sleeping patterns? What would happen?


3 Answers 3


Using humans who live above the Arctic Circle as an example, they would do just fine by making their own night and day at the time intervals their circadian rhythms dictate. They would use blackout shades to cover the windows and artificial illumination to create daylight when they need it. Without the ability to create artificial day or night, things could get ugly fairly fast. There's a lot of research floating around the Internet on what happens to Arctic inhabitants and research into modifying sleep cycles using a process called entrainment. Most subjects seemed to feel better on the 24-hour cycle though.

If the humans lived on that moon for thousands or tens of thousands of years then they would adapt to the longer days and nights (though perhaps with some residual memory of the 24-hour cycle?). If there is some kind of selection pressure that adapting to the long days somehow increases chances for survival, then I would expect the adaptation to happen a bit faster.

Given a wicked advanced set of genome engineering, then it may be possible for the humans to adjust their circadian rhythms without the resorting to the selection pressures of evolution. This is a mind boggling degree of power because those rhythms touch so very many systems.


We don't sleep about 7-8 hours due to the night on our planet. We sleep that amount since our body needs that. Or, to be specific, our brains seem to need sleep. Our bodies outside our brains would be fine by simply lying around and rest. But without sleeping our brains will start to act weird, we cannot create memories, our level of consciousness changes. Based on animal tests after 18 days of being nonstop awake, we start to drop dead.

Thus regardless of the amount of day or night time some planet might have humans need that 8 hours of sleep to operate for the next 16+ hours. How much there are light or darkness may disturb some individuals ability to sleep well, but the overall need for sleep remains the same.


As to your question, "how would humans react?" I think you have to remember that humans are intelligent, pattern seeking planners. If they have clocks, they are going to design a sleep schedule most similar to what they are familiar with, where they are awake for as much of the daylight as possible. Since 96 is divisible by 24, that shouldn't be hard. They'll probably get less sleep on nights where the sun is up, and sleep longer on days without sunlight.

Your moon would have time zones, in that the sun comes up and goes down at a different time all around the globe. The eclipse will happen at different times of day in every time zone. On half of the planet, the eclipse will happen at night and it will be like it isn't there at all. But, since everyone needs to sleep twice during each day and sleep twice during each night, a global society on this planet might agree to all wake and sleep on the same schedule, so the society might not use time zones.


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