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I want to create a planet where there are extreme winters (3 months with temperatures up to -40°C) at around 50° latitude. The summers are just slightly hotter (a day of 30°C in the summer would not be unusual).

The size of the planet is the same as earth. What would the orbit and axial tilt be like to make this seasonal pattern possible?

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    $\begingroup$ You've obviously never spent much time in Canada :-) Or even the US states adjacent to it. Record lows for a few states: Minnesota -60F/-51C, Montana -70F/-56C, Idaho -60F/-51C, New York -52F/-46C, Maine -50F/-45C... IOW, Earth fits your specified conditions. $\endgroup$
    – jamesqf
    Commented Mar 5, 2021 at 17:26
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    $\begingroup$ This is natural for highly continental climates. On the Earth, we are close to it (-40 for 3 month), but not quite there in places like Southern Siberia, Mongolia and Northern Kazakhstan. Would you be Ok with "continental" solution, or you'd like to have +30 to -40 seasonal swings near the coastlines? $\endgroup$
    – Alexander
    Commented Mar 5, 2021 at 18:53
  • $\begingroup$ Yeah, this is just Earth. $\endgroup$
    – rek
    Commented Mar 6, 2021 at 5:44
  • $\begingroup$ What I see written is temperatures up to -40 C. Not down to. So whatever this is ... it's not Earth. $\endgroup$ Commented Mar 6, 2021 at 17:04
  • $\begingroup$ Thanks for all your input. I would like to have these temperatures near the coastline. I would also like the duration of the seasons to be more or less the same. The goal of this weather pattern is that these extreme temperatures (during winter) force the inhabitants of my world to go underground for +- 3 months. $\endgroup$
    – KjVdB
    Commented Mar 8, 2021 at 7:24

2 Answers 2

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This is the orbit you need:

enter image description here
(x 1,000,000,000m)

So as L.Dutch beat me to saying, you need to make the orbit more eccentric. To show it visually; the earth is the orange ring currently. Move it to the green ring or maybe the blue ring.

enter image description here

if 0 is a perfectly circular orbit, and 1 is an escape orbit, earth is currently 0.0167, with min and max distances of 147gm (gigameters) and 152gm, and an average of 149.5gm

50 degrees north seems to get winter max temps of 5-7 degrees, to get winter maxes of -40, you need to take 45 degrees off the winter temp. From about 278 Kelvin to 233 Kelvin, a 16% decrease in temperature.

As a simplification, we can just approximate that at ~9% further increase in distance will give a ~16% decrease in temperature.

So you want an orbit that gives 146gm (slightly closer as you want slightly hotter summers) and 166gm, using this calculator I calculate you need an eccentricity of 0.064103 and an average distance of 156.

This would also cool the Australian summer and shorten and warm the Australian winter - that sounds quite nice.

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  • $\begingroup$ In your chart of "what you need". It would be good if it also included earth standard numbers for easy comparison. e.g. header columns: parameters, Earth, proposed $\endgroup$ Commented Mar 5, 2021 at 19:18
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You need to make the orbit more eccentric, so that the winter in the North emisphere corresponds to the period of maximum distance from the sun, while the minimum distance happens at a distance comparable with the one of our planet to the sun.

Summers will be shorter, because the closest the planet to the star, the faster the orbital velocity.

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  • $\begingroup$ Might be worth noting that whilst this fulfils the "cold northern hemisphere winters" it also makes the southern hemisphere pretty chilly, too. Just fractionally less so. $\endgroup$ Commented Mar 5, 2021 at 22:31

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