Sunset Dec 21 at Fairbanks, latitude 64 degrees 50 minutes. Photo taken about 2:40 pm, looking a little west of south.

Happy Southday! (Or, if you don’t follow time as measured on the planet Central, Happy Winter Solstice.) The days in the northern hemisphere are getting longer again!

Solstice has nothing to do with distance from the sun. In fact, we are rapidly approaching our closest approach to the sun, around January 3. But because the earth’s axis is tilted relative to its orbit around the sun, there are times (the solstices) when one pole or the other comes as close as it ever gets to pointing directly at the sun, while the other is as close as it can get to pointing away. That happened on Dec 21 this year with the north pole pointing as far as it could get away from the sun.

On the winter solstice, the sun never rises north of the Arctic circle, while it never sets south of the Antarctic circle. Closer to the equator it rises and sets, but the northern hemisphere days are at their shortest for the year, and the sun at noon is at its lowest in the sky. The low sun and short days combine to minimize the solar heating of the ground and water. The opposite is true in the southern hemisphere, where it is the first day of summer, and both day length and solar elevation are at their greatest for the year.

Our Earth’s axis of rotation is 23.5 degrees from axis of rotation of its orbit around the sun. What would happen if that angle were 0?

I actually invented such a planet, called Eversummer, for my second science fiction novel, Tourist Trap. It wasn’t exactly paradise!

The planet’s name, Marna thought, must have been picked out by a publicity agent.  Everspring would have been more accurate, or Everfall, or perhaps Constancy.  Maybe even Boredom.

The planet, with its rotational axis almost perpendicular to its orbital plane, had no seasons.  The poles were bitterly cold, glaciated wastelands where the sun forever rolled around the horizon.  The equatorial belt was an unchanging steam bath, the permanent home of daily tropical thunderstorms, varied by hurricanes along its poleward borders.  The desert belts, inevitable result of the conflict between the planet’s rotation and its unequal heating by its sun, were broad and sharply defined, with no transition zones where the rains came seasonally.  The temperate zones, between desert and polar ice, were swept year round by equinoctial storms, varied only by occasional droughts.  No monsoons, no seasonal blanket of snow to protect the dormant land, no regular alternation of wet and dry seasons.

Would you like to live on such a planet?

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