# What would it take for a continent to be covered in cyclical darkness?

I'm contemplating a world in which there is some sort of cyclical darkness that covers a continent or the whole planet, and humanity has to adjust to deal with the creatures that surface when the darkness comes.

Something more than just the day/night we have on earth. Perhaps the lunar cycle is closer. For example, every 28 days the planet (or a continent) is covered in darkness for 3 days.

I'm not referring to one side of the planet permanently being dark, such as a tidal locked planet.

Other than astronomical causes, would there be anything else that could cause this? Fog? Haze?

• Please, ask one question a time. Now you ask for both cause and result of this darkness. Trim this to cause, and when you will have cause figured out, then ask a follow up question about results for life and civilizations. Possibly in a way bit narrower than now. – Mołot Jan 18 '17 at 15:32
• If the moon were closer it would need to orbit faster so it wouldn't take 28 days to complete it's cycle anymore. – Lio Elbammalf Jan 18 '17 at 15:35
• just slow the rotation of the planet and you can get three days of light and three days of night. moving the moon will not do much. but you might want to split this into two questions one about how an another about lifeforms. – John Jan 18 '17 at 15:36
• Agree with @Molot, the last paragraph is too broad for a single question. How could you expect someone to answer all that in 500 words or so? You should eliminate that last paragraph or this will be closed as too broad. – kingledion Jan 18 '17 at 16:14
• Edited to one question, appreciate the feedback. – eldfell Jan 18 '17 at 21:45

I can see a few plausible solutions.

1 - Binary planet. A similar setup as Pluto and it's largest moon Charon...During parts of the orbit, Charon casts it's shadow upon pluto. The orbital period of the planetiods around each other will determine the length of this 'lunar eclipse'. Not quite functional in Earths setup due to how much smaller the moon is here.

2- Harsh planet tilt. Earths seasons come from the fact the earth wobbles back and forth during it's orbit. At around 75 degrees (north or south) you get to see a single sunrise and sunset (thats 24 hour darkness to 24 hours daylight). Had this tilt been more severe (tropic of Capricorn is at 60 degrees not 22.5) and happen more rapidly, you could have this effect.

Local phenom that could cause this is harder to justify it's consistency. Volcanic cause nuclear winters are based on a volcanoes eruption, which could be constant but more likely it's irregular and not easily predicted. There's some options that could see a persistent large sized cloud slowly roam the planet as well, but once again...hard to justify.

You could have massive volcanic eruptions and regularly create a temporary volcanic winter

• Damn. Beat me to it. – AngelPray Jan 18 '17 at 16:53

Planet Kepler-47c orbits two stars. It goes all the way around a binary system. That means that the star it sees changes over the year. If you have a planet like that, you could make one of the stars bright and the other dead/dim. The period of orbit is pretty long... takes a while to get around both stars, and your planet has to be far out to have a stable orbit, but it achieves the dark part of your question. Your on your own for life effects... not my department. :-)

http://www.space.com/29985-is-life-possible-around-binary-stars.html

A lot of flowers close at night, maybe you could have mushrooms or something that sprout out of cracks in the ground during the dark period? Also you could have a sandstorm or something similar that has some sort of light substance carried extremely high up, blocking any and all light. In the Arctic and Antarctic I think they sometimes have long periods of darkness so you might want to check there.