Re: equinox

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Nik Taylor wrote:

>Another possibility - a planet with a very eccentric orbit, replacing
>tilt as the primary cause of seasons, if it's eccentric enough, there
>could be migrations from the equatorial regions to the polar regions
>over a yearly basis.  Or, a planet with such a long orbit (orbitting a
>supergiant, perhaps), that it's "year" is, say, 80 of ours, so that a
>person would be lucky to live one year!  Or some science-fiction author
>(I don't remember who) based his stories on a planet orbitting a
>double-star, the second of which orbitted in a centuries-long orbit
>around the primary, getting extremely close at the perstellon and
>extremely far at the apstellon, creating "seasons" of centuries in
>length.
It seems very similar to LeGuin's "Exile Planet", that I just commented, =
but it's different enough to presume you're talking about something =
else. Couldn't it be Robert Heinlein's "Double Star"? (I've not read it, =
I just remember the title).

Yet another possibility would be precessional change. I read about Mars =
and precessional seasons in a book by Carl Sagan. The axis of the planet =
revolves around a theoric axis and this causes the axis to vary its =
inclination. The cycle is very slow, about 25,000 years to complete a =
circle. When the axis is very tilted, the winters are cold enough to =
freeze most of the CO2 in the atmosphere. But in the least-tilted =
position, the Martian seasons would tend to become equal, and in the =
tropics there could be a temperature over zero degrees for a period long =
enough to avoid CO2 from freezing. The gas would begin to melt on the =
poles, and we already know when you throw large quantities of CO2 in an =
atmosphere... I once wrote a short description of this process and what =
the Martians did: the whole race prepared for the Long Winter, building =
(millennia beforehand) immense installations to hibernate and wake them =
up automatically after 25,000 years. I might take that up again now that =
I think of it -- at that time I was really bad at writing stories (not =

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