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The project that I'm currently working on involves a Binary Planet system, both with life, although I'm only focusing on one. This planet has a climate similar to Earth, aside from the temperature regions due to no seasons. (which I've already kept in mind for plant life) Also since it's a binary planet, half of the world would have light reflected by the sister planet at night, while half would be extremely dark, possibly even pitch black.

Would a day length of 80 hours be long enough to see a noticeable effect on plant life? Since plants get energy from photosynthesis, I would assume that longer nights could hinder them somewhat, but I'm not sure if that would be sufficiently different enough to change how said plants would function.

From another question I found, someone said plants would need larger sugar-stores to make up for the longer period of no sunlight, but aside from that most questions are geared towards several week/ month long days rather than slightly longer ones.

  • $\begingroup$ How much of this 80-hours is "light", and how much is "dark"? Also, consider checking out plant-life in countries that experience midnight sun, such as Norway - although, those all tend to be explicitly cold climates. $\endgroup$ Jan 14, 2019 at 8:57
  • $\begingroup$ @Chronocidal the days are split up by 40 hours/ 40 hours, and since the planets orbit each other with ~no tilt the days stay the same length (give or take a few minutes/ seconds) for the whole year. At the poles it would be twilight all year, however it's a permafrost zone so plants wouldn't exist there anyways $\endgroup$
    – Foosic17
    Jan 14, 2019 at 15:59

2 Answers 2


You can look at Earth and see what happened. During the Mesozoic and into the Cenozoic, you had forests going to the poles, and thus plants experiencing long days (literally months long) at times and long nights at the other extreme.

No huge change in plants are required. There's no significant difference in fossil plant assemblages compared to plants found at lower latitudes, taking into account temperature differences. The plants adapt to the longer days/shorter nights (and the reverse) without requiring any significant changes.


Greater mobility

Plants will probably move when night falls and use the ground as shelter (because longer nights means cooler nights and hotter days) For animals the same thing most if not all animals will probably seek shelter in the night.

Depending on the temperature of your planet it could also be the other way round in the night everything comes to life and in the day it is to hot so every thing seeks shelter from the heat.

Even when your plants open up in the night because the day is to hot they could use photosynthesis from the other planets reflection.

Further Information

For any other thing that could happen look here. (Yes this is longer and thereby your effects will be smaller (winds instead of storms) but still you could apply some of them)


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