May 27, 2024


Science It Works

Classic SF Featuring Planets With Very Long or Very Short Days

Earth is blessed with a day neither of extraordinary length nor of extreme brevity. Currently it is about twenty-four hours long. A quick glance at planets like Mercury and Venus shows us that worlds can have days much longer than Earth’s; bodies like Haumea suggest that days could be much shorter.

SF authors have notice this and written books about planets/planetesimals with different day lengths. Consider these five vintage works.


Mission of Gravity by Hal Clement (1953)

61 Cygni’s world Mesklin is sixteen times more massive than Jupiter. A day less than twenty minutes long means that the gravity at the equator is a measly three gravities. Thus, human starfarer Charles Lackland is able to briefly set down near the equator, where he is subjected to extreme discomfort (rather than immediate death). Too bad for Lackland that the object of his quest, a lost probe, is near one of Mesklin’s poles, where gravity is high enough to reduce a human to paste.

Conveniently for Lackland, Mesklin is not only life-bearing—it has natives. Rational self-interest being universal in Clement’s universe, Lackland strikes a deal with local trader Barlennan: retrieve the probe in exchange for services only someone with space flight can provide the trader. What follows is a glorious expedition through conditions quite alien to the human reader.



Hothouse by Brian W. Aldiss (1962)

Eons from now, the Earth’s rotation has slowed to the point that one day lasts a full year. Consequently, the Sun is fixed in Earth’s sky. The plants on the sunlit side of world have flourished. They and not animals are now the masters of the world for as long as the Sun shines. It is a golden age…provided one is an enormous banyan tree. For humanity’s pitiful descendants, it is anything but a golden age.

Now merely food for more favored species, the handful of primitives who prevail have knife-edge margins of survival. There is no room for charity.

Convinced that the adults are too old to protect their children, tribal leader Lily-yo divides the tribe. The elders will travel up, exploring what waits at the other end of For their part, the children will explore the potential of internecine squabbling in a deadly environment.



Still Forms on Foxfield by Joan Slonczewski (1980)

Foxfield’s Quaker settlers were attracted to the planet by its proximity to the Solar System. Tau Ceti is one of the nearest stars. It’s inviting to a group of pacifists fleeing a doomed Earth in a previously owned sublight starship. Convenience comes with a price. Foxfield’s biochemistry is indigestible for terrestrial life, and the day is over forty hours long.

Rather than try to stay awake for the full day, the human settlers instead adopt mid-day sleep. Whether they could have handled the world’s other peculiarities is moot. Foxfield is home to indigenes who, while very alien, seem fond of their new human neighbors and willing to help them survive.

It’s a very happy story until the day a United Nations Interplanetary starship appears in orbit. Earth was not doomed after all and it is determined to put Foxfield its proper place under the UNI’s benevolent guidance. Declining this gracious offer is not an option.



West of January by Dave Duncan (1989)

As unhappy colonists long ago discovered, their target world was almost, but not quite, tide-locked to its star. It takes the world 264.6 days to orbit once. It takes 263.6 days to revolve once. Instead of an endless day on one side and endless night on the other,

The consequences for the settlers are profound. Climates and biomes are transformed as the sun slowly rises, and just as slowly sets. The settlers have lost all but the most primitive technology in their endless migrations across their inexorably changing world. Life is hard and short.

Knobil seems likely to live a life even shorter than most. A chance encounter with an angel sets the young man on an altogether different path.



Nightside City by Lawrence Watt-Evans (1989)

Nightside City was founded under the mistaken impression that Epimetheus was tide-locked to Eta Cassiopeiae A. Had the planet been tide-locked, everything would have been fine (for barely habitable values of fine). In fact, the terminator between day and night advances at one hundred and thirty-eight centimeters a day.

As so many things are, certain doom is unevenly distributed. Nightside’s West End will burn before the East End. Unsurprisingly, those who can promptly move from West to East in a bid to extend their lives. West End real estate is clearly worthless. Why, then, is someone buying it?



No doubt there are many examples I could have used but did not. Feel free to remind me of them in the comments.

In the words of Wikipedia editor TexasAndroid, prolific book reviewer and perennial Darwin Award nominee James Davis Nicoll is of “questionable notability.” His work has appeared in Publishers Weekly and Romantic Times as well as on his own websites, James Nicoll Reviews and the Aurora finalist Young People Read Old SFF (where he is assisted by editor Karen Lofstrom and web person Adrienne L. Travis). He is a four-time finalist for the Best Fan Writer Hugo Award and is surprisingly flammable.