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I'm writing a setting for some fantasy novels, and came up with an idea about weather and climate.

The world I'm imagining has an elliptical orbit around a binary system, giving it basically 2 stars. My question however regards the seasons cycle. The way I've drafted it is that such a planet would perform a complete orbit around the stars in 4 years.

By year, I mean a cycle of 12 months, with 4 seasons.

Now, as the planet reaches apoapsis it would enter a "winter year", meaning a year with 4 season, but far colder, and as it reaches periapsis it would enter a "summer year", a year with higher average temperatures, and inbetween those years, a spring and fall years, in which temperatures get progressively warmer and colder respectively.

Would such a setup be possible?

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  • $\begingroup$ Not a duplicate because your planet orbits two stars and not one, but very likely relevant nonetheless: How do seasons work in a binary system (planet orbits one star, not both)? $\endgroup$ – a CVn May 17 '16 at 15:01
  • $\begingroup$ A year is typically defined as one orbit. So, an orbit lasting 4 years sounds a bit strange. $\endgroup$ – MichaelHouse May 17 '16 at 15:20
  • $\begingroup$ So, for clarification, you mean the planet circles the binary stars once in 1460 days (four "years")? And four seasons in that single orbit? $\endgroup$ – Mikey May 17 '16 at 17:15
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    $\begingroup$ For a more extreme cycle around a binary star, maybe see Helliconia Spring/Summer/Winter where each novel is set over a season. The seasons in that setting are longer than human lifetimes. $\endgroup$ – Neil Slater May 17 '16 at 19:13
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No, the length of the year has no effect on the seasons other than their respective duration.

Seasons are caused by the axial tilt of the Earth, not by the length of the year. The length of the year only determines how long the seasons are in absolute terms, but their relative duration would still be the same. Spring would still be a quarter of the year, same as summer etc.

That being said, Earth's axial tilt does vary over time, on a ca. 40,000 year cycle, with the moon acting as a stabilizer. If you design a world with a much longer year and a much shorter axial tilt cycle, you could make your variable seasons per year work.

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    $\begingroup$ Having a highly ellpitical orbit and something to cause a axial tilt to fluxuate every 6 months would work, though it would probably be fantasy only. WIth enough of an eliptical orbit, it could be argued the extra variable distance would be able to make a significant difference in temperature, then the axial tilt is the 4 seasons, and the distance determines if the 4 are its cold, warm, or hot. It would have shorter Hot seansons though due to the orbit, but if the orbit itself is massive (presumably around a massive star), the difference can be mitigated. $\endgroup$ – Ryan May 17 '16 at 16:03
  • $\begingroup$ This answer is correct for earth, but there are alternative set ups. $\endgroup$ – PCSgtL May 17 '16 at 17:39
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yes you can have something like that. they are called superseasons

We have them on Pluto. Also here.

It's basically what you describe; you have seasons within seasons, like a "cold winter" and a "hot summer" etc. Both tilt and distance affect seasons on Pluto.

I think it's going to be hard for you to have something like that for a planet in the goldilock zone; its orbit would have to be extremely elliptical (something unusual for an inner planet).

But maybe you can have the same effect with a different solution. Change your planet into a moon! If your planet is a gas giant moon its axial tilt can cause the "miniseasons" that last maybe 1 month, and then either the distance from the star or the seasons (determined by the axial tilt) of the gas giant can be the "superseasons"

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First, with the reality-check tag, I'm not sure you could have a 4-year orbit around a pair of stars and still be within the "Goldilocks Zone" of the system.

Here is a rough set-up that could allow multiple groups of seasons within the same solar year. This does require the suns be far enough apart for their mutual orbits to have a period a significant fraction of the orbital period of the planet. The set-up is much easier to visualize if the periods are in resonance so that each planetary year matches up with a set configuration of the suns during its orbit. Distance from the suns may have a slight effect on seasons, but the primary driver will be the regular eclipsing of each sun by the other. I believe this would be most visually distinctive with two suns of about the same size, but of slightly different colors.

Your planet is in a significant elliptical orbit around the stars. Start its orbit at the apogee and sync up the suns so that one is eclipsing the other (only one sun in the sky). Also have the tilt of the planet align with the suns. For the hemisphere tilted away from the suns (call it north), this will be your coldest time of the year. The hemisphere tilted towards the suns (south), though technically in "summer", with only a single sun in the sky it will be relatively cold.

Move the planet 1/8 of its orbit. There are now two suns in the sky at their farthest visual distance from each other. This is summer. Two suns in the sky warm the planet more than a single sun, regardless of axial tilt.

Move the planet 1/8 of its orbit. The suns are in eclipse again and winter is back.

Another 1/8. This will be the "hot" summer for the north with 2 suns, closer orbit, and tilting towards the suns.

Another 1/8. The perigee of the orbit, with the north tilted directly at the suns. Luckily the suns are again in eclipse, so it is winter, but a "warm" winter.

The next 4/8 will be a mirror of the first, moving back to the apogee.

You could introduce additional differences by having one star emit more infrared or ultraviolet and note the differences that would make when one would eclipse the other.

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  • $\begingroup$ The "Goldilocks Zone" itself has little to do with the amount of time it takes for a planet to orbit a star. The zone is defined as an area where the temperature is warm enough where the elements required for an atmosphere that can sustain life are in the correct state, but not so hot as to boil the atmosphere off into space. Our sun is relatively small compared to many other stars. It would be in the realm of possibility that in another solar system, the star is significantly large enough where the planet has an orbit which is much larger/longer than ours, but still remain in the correct zone $\endgroup$ – Jason Hutchinson May 17 '16 at 18:17
  • $\begingroup$ Yes. My statement was referencing the probability that a 4 year orbit will likely be too close to the binary. I could be wrong. $\endgroup$ – Michael Richardson May 17 '16 at 18:20
  • $\begingroup$ With the elliptical path, it may be possible. Although, the eccentricity of the orbit could not be too high because the planet would travel too far away/close to the star which would mean that the planet could not essentially sustain life. It would be far simpler if the binary star system was not in play. $\endgroup$ – Jason Hutchinson May 17 '16 at 20:02

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