In a world I am building, the planet's days are longer than its years, with a single day taking 9 years. In all other ways, this planet is similar to Earth, but are there other differences I am missing?

Weather has played a massive role in history and science. It creates jungles; it creates deserts. Weather decides the biomes of a landmass above all else, which makes me wonder: on a planet where every day lasts 9 years instead of 24 hours, what does the weather look like?

  • $\begingroup$ This sounds like another planet we know. On Venus, a year is 225 Earth days and a day is 243 Earth days. $\endgroup$
    – The_CIA
    Commented Feb 10, 2017 at 1:52
  • $\begingroup$ You’re not a noob so I’m asking about your punctuation in the title rather than just editing it. ? vs ^ aren’t usual typo error. $\endgroup$
    – JDługosz
    Commented Feb 10, 2017 at 9:59
  • 3
    $\begingroup$ @JDługosz my computer is a piece of garbage that for reasons unknown to me decides that I really need the keyboard set to French Canadian. In which I need to shift type 6 to get ?. kbd-intl.narod.ru/images/ca-intl.png Unfortunately, it also thinks that I need some chaos and switches between the two at random. I usually catch it. $\endgroup$
    – TrEs-2b
    Commented Feb 10, 2017 at 10:30
  • $\begingroup$ The weekly forecast would be... interesting. $\endgroup$
    – PatJ
    Commented Feb 10, 2017 at 13:37
  • $\begingroup$ @TrEs-2b just reinstall Linux. Excuse to try a different distro. $\endgroup$
    – JDługosz
    Commented Feb 11, 2017 at 1:24

3 Answers 3


@Alexander is correct. Let me elaborate.

Diurnal hemisphere (day side)

  • Extremely hot
  • Little precipitation or clouds (it'll dissolve once the water becomes a liquid) over the continents, but likely a lot above the sea (increased evaporation)
  • Warmer seas. These won't completely evaporate as water will be able to flow in from the cooler regions, replenishing them.
  • Incredible ocean currents. One side of the day zone will always warm, adding water to the sea, while the other will always cool, removing (liquid) water. This is bad news for any inhabitants that want to move with the habitable zone: if they meet an ocean, they'll have to traverse its waters head-on.
  • Little wind, as most areas will have equal pressure
  • Little surface vegetation or surface-dwelling life
  • Don't expect a "sandy" desert, expect landforms as usual! Massive amounts of sand come from weathering and erosion, which are area-specific and not necessarily related to temperature.

Nocturnal hemisphere (night side)

  • Extremely cold
  • Little precipitation (it'll be a cold desert, like Antarctica, because all liquid water will fall once it arrives at the edge)
  • Extremely cold seas, with abundant (though not necessarily widespread) ice / glaciers
  • Snow cover. Despite the lack of precipitation, some snow will fall when the region enters the "cold zone" and a steady temperature will maintain it. This has an interesting effect: most footprints will be preserved for 4.5 years.

Habitable belt

  • Extreme wind! Cold and hot air will meet and constantly exchange, resulting in constant and strong currents.
  • Precipitation! The combination of hot and cold fronts, combined with the fact that this is the only place where liquid water will like to exist, will bring torrential downpour.
  • Weathering and erosion will be widespread. Nearly all rainfall happens here, as does The Great Freeze (cracks apart rock) and The Great Melt (moves sediments). This is the best place to reshape the environment quickly.
  • Most plant life will reside here, because water is accessible. Plants will grow at an extreme rate away from the sun and toward newly exposed land, because staying put will mean burning. Alternatively, they will bury their seeds, reviving to grow and reproduce at each intermediate period between the heat and the freeze. Plant roots must adapt, as rapid erosion means less material to hold on to. They must either grow downward constantly to maintain a grip, or grow much further down the first time.
  • Animals will develop an instinct to do the same thing - dig and hide or constantly stay on the move. Anything that can't cross the ocean, go around it, or bury itself is screwed evolutionarily. Flying creatures should be OK.
  • More information can be found here


  • Average temperature (always a meeting place of warm and cold air, as opposed to only once every 4.5 years)
  • Heavy precipitation and extreme winds
  • Widespread weathering and erosion
  • Abundant plant and animal life; possibly the best place to start a permanent civilization

For a more general overview of winds, see here.

  • $\begingroup$ Please edit to add a link to Alexander's answer so if the two get separated by other answers, it's easy to find. $\endgroup$
    – SRM
    Commented Feb 10, 2017 at 13:37
  • 1
    $\begingroup$ Thank you for a very detailed answer. I would, however, disagree with couple of point - no precipitation and little winds on day side. If we have an oceanic planet like Earth, hurricanes will be forming continuously. They derive their power from a vertical gradient of temperature, which should be significant, and they should be traveling (with all the wind and rain associated) across the day side until they meet a continent. $\endgroup$
    – Alexander
    Commented Feb 10, 2017 at 19:56
  • $\begingroup$ @Alexander Fair point. I'll edit in a bit. $\endgroup$
    – Zxyrra
    Commented Feb 10, 2017 at 20:19

Your day side will be hot, and night side - quite cold. There will be a lot of winds blowing from night side to day side. Depending on the amount of water, there could be torrential rains in some areas. However, 4.5 years night is not enough to form sizable glaciers except at high latitudes. Overall, things would not be as extreme as in case of a tidally locked planet.


Society on your world will evolve in ways quite different from Earth.

The people on your world will have to have some means to navigate that doesn't rely on either the stars or the sun. If there is one or more moons that are visible during the day and have rapid movements, then that might be used to establish east/west or north/south. Otherwise, the sun moves too slowly to do anything useful with. Remember, China didn't use compasses to navigate until somewhere around 200 AD while Europe didn't adapt to compasses until much later. Latitudes were originally measured by noting the height of the sun at noon. This method won't work in your world. Longitude will be just as difficult, I imagine.

Societies would probably remain more mobile than modern society as they chased the habitable belt around the globe.

Given that seasons are probably more closely tied to the long day than the short year, the concept of a year may never figure into their concepts of time tracking. The "day" would be their long measure instead.

The stars would be less likely to have religious/social meanings to this world than they do to our ancestors.


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