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Essentially I'm looking for a plausible way that a planet could have odd, extreme seasons. Basically I'm wondering how (or if) a planet could work that has a week long day during the summer and a week long night during the winter. You guys can get as crazy with it as you want to I just can't figure out a way to make it work.

(Can mess with obliquity, rotation rates, eccentric orbits, etc. whatever works)

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  • $\begingroup$ Worldbuilding != crazy; //just saying $\endgroup$
    – user6760
    Nov 26 '19 at 4:54
  • $\begingroup$ do you want the entire planet to have this week-long day, or just some certain parts? do you want it to be an annual phenomenon, or something that happens monthly? $\endgroup$
    – Thỏ Già
    Nov 26 '19 at 5:59
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The easiest way to achieve this is through Axial Tilt and be closer to the poles. In point of fact, we already have this on Earth due to our own axial tilt. This is the same attribute that causes the seasons on Earth.

Demonstration of Seasons and Daylight due to Axial Tilt

Looking at this picture from the second link above you can see that at certain times of the year, the closer to the poles you are the longer the daylight is shorter the night is during Summer, and the reverse is true in Winter.

This is not to say that the length of a day in terms of the rotation of the earth is concerned; a 'day' by that definition is going to be exactly the same. But, if you define a day as being that period of time during which it is light once and dark once due to the position of that point on the planet with respect to the Sun, then during Summer and Winter you will have longer days, that have proportionally much longer light and dark periods respectively.

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Welcome to world building.

Actually it’s quite a simple problem if the planet has a slow rotation rate. If it takes 14 Earth days to make one complete revolution then it will have one week “days” during the summer and a one week “nights” during the winter. Incidentally it will also have one week “nights” in the summer and one week “days” during the winter, so its “days” and “nights” are always one week long.

To have the same effect across the whole planet it would be necessary to have a 0 degree axial tilt rather than the 23 degrees Earth has. Highly eccentric orbits might cause some disturbance due to motion of the planet covering a significant distance in one week putting the timings out. A circular orbit wouldn’t have this problem but wouldn’t have seasons either.

If the intention was for 1 Earth day “days” and 1 Earth week “nights” in the winter and the reverse in the summer then unfortunately it is not possible because a planet can’t be speeded up or slowed down as quickly as you need due to the amount of rotational energy involved and the law of conservation of angular momentum.

Assuming that the effect is needed to be planet wide and uniform. If not then the situation arises on Earth already.

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Yet another possibility is a combination of two things:

  • Planet's axis of rotation lies in the ecliptic or not far from it
  • Planet's sidereal year is more than four weeks long

Twice a planet's year the end of it's axis will point at the system's sun. One hemisphere will at that time have a week long day, the opposite one - a week long night. During a week in between seasons day and night will change normally everywhere on this planet. If you wish for even longer nights, you can extend the planet's year.

What else should be considered:

  • Shorter revolution periods are possible when planets are close to their stars. If you wish this planet to have four week year and be in Goldilocks zone, you should assume that the star is a low luminosity red dwarf of type K or M. This in turn means its spectrum is severely shifted towards infrared. Planets surface will feel very dim for us regular humans. The longer your year, the brighter star you may have, since it will move habitable zone further away from the star.
  • Week long days and nights (like those during four week year) do not necessarily mean extreme seasons. Thick atmosphere and large oceans can balance out temperature variations quite effectively. You may wish to make them even longer, but the other extreme may lead you to boiling oceans and freezing atmosphere at some point.
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