# Could this planet exist?

I've been thinking of a planet where the day/night cycle is way off to where there 30-35 hour long night period, while there are only near 8-4 hours of daylight. The local biological environment is hostile, twisted by some kind of contagion, thus, forcing humanity indoors. If this planet could exist, and humans colonized it, would they be able to survive in the altered day/night conditions, and with not being able to leave their colony?

~Thanks!

• Related question: worldbuilding.stackexchange.com/questions/135649/… – Logan R. Kearsley Jan 7 at 4:17
• Keep in mind that Earth experiences different lengths of days and nights all over the planet. If we had 0° tilt, you'd have a 12hr/12hr day at the equator and permanent daylight at the poles. Due to our tilt, those poles tend to see months of daylight and night. So, clarification #1... since it's impossible to experience this planet-wide... where on your planet are you experiencing it? – JBH Jan 7 at 4:37
• Hint for answerers: One possibility is to assume that there are habitable zones on the planet, where the condition of the ~1:4 day/night cycle would match. The rest could be inhabitable for any reason, including the cycle. – Battle Jan 7 at 15:20

There is a recent similar question:

As my answer says, different latitudes on Earth have different daylight/dark night radios at the same time, and any specific latitude on Earth has different daylight/dark night radios at different times of the year.

So getting a specific daylight/dark night ratio all over the planet and during every day of the year could be very difficult.

All planets have some amount of axial tilt or obliquity, which is defined as having a possible range from 0.00 degrees to 90.00 degrees.

If the planet has an axial tilt of nearly zero degrees - the eight planets in our solar system have axial tilts ranging from 0.03 degrees (Mercury) to 82.23 degrees (Uranus) it won't have noticeable seasons and the daylight/dark night ratio will not change over the course of the year. And I don't think that different latitudes would have different daylight/dark night ratios in such a situation either.

But the constant daylight/dark night ratio on such a planet would normally be 1:1 instead of the 4:35 (or 0.114) to 8:30 (or 0.266) ration you ask for.

There is a simple geometric reason why normal stars illuminate half of a planet's surface at any one time.

The planet Earth has a diameter of 12,742 kilometers, the Sun has a diameter of 1,391,400 kilometers, 109.19 times as great. So if the Sun and the Earth were touching, the Sun would illuminate a lot more than half of the Earth's surface at any one time. The farther away the Sun was from Earth, the smaller the proportion of Earth's surface it would illuminate at any moment, But even at infinite distance the Sun would still illuminate at least half of the Earth's surface at any one moment.

So any normal Earth like habitable planet orbiting any normal Sun-like star at any normal distance necessary to be in that star's habitable zone is going to have very slightly more than 50 percent of its surface illuminated by that star at any one moment.

So I guess you should look at my answer to this question Day/night cycle science help?1 and see if you can use any of my suggestions modified for your desired light/dark ratio.

I don't think that a planet with a planet-wide day-night cycle where the night is 5x to 10x the length of the day could exist, at least not for very long and all over the planet, but let's take it as given.

Not being able to leave their colony would actually be an advantage, since the wild day/nigh cycle would produce extreme weather conditions. All of the heating would occur during the 4-8 hours of daylight, while there'd be 30-35 hours of cooling. It would not necessarily be cold, but there'd be a big different in day and night temperatures. It seems likely that the planet would be quite inhospitable during day or night (or both), necessitating shelter.

The day/night pattern and length would wreak havoc on the human circadian rhythm, probably forcing people to have an artificially-lit "day" in the middle of the 30-35 hour night. Again, working mainly indoors would help.

I very much doubt that 30-35 hours of darkness would be good for plants, either, so they'd probably have to rely on hydroponics.

It really makes you wonder why they didn't stay in a nice, clean, safe space station...

You could have something like this if the colonized areas are at the bottom of deep north/south running valleys. The sun would only shine down onto the colony during a smaller part of the day. You would have dusk like conditions during many of the daylight hours that the sun does not shine down into the valley.

Edit -- Many of the other answers go into the many reasons the actual day/night cycle would not be very stable in a situation where night is 3-5 times longer than the day. Here is a way to look at the planet itself to see if there is a way to get a similar result geographically.

• This is an excellent answer, and was what I myself was going to suggest. Good to see someone beat me to it. :) – Arkenstein XII Jan 8 at 1:35

It would be much easier to have the opposite exist. If such a planet orbited a binary star, if the orbit past between the stars, the day would last longer, coming from one or the other star.

Now, if the planet was tidally locked to one star and it had a very quick orbit around its primary parent star, the secondary star would provide day for the dark side of the planet. So if the parent star is a small red dwarf and the planet orbited ~0.05 AU away, it would be tidally locked and with an orbit ~4 days. If the secondary star is a main sequence star and is >1 AU away, lets say ~2 AU, it would visible to any part of the dark side of the planet for ~ half its "year" but would have very little effect or lamination for a small portion of that rotation.

However, for the planet to be survivable, the parent star would have to be extraordinarily weak and the planet would probably have to be a super earth. If you add in the possibility of this super earth as a moon of a Jupiter (or bigger) world, the orbital dynamics may be favorable to this night/day cycle, which I would not be able to figure out the math on that one. Hope someone here could figure that one out.

• The day-night cycle for the orbit you describe would still be 1:1 except for the eclipse when the primary is between the "sun" and the planet of the question. To have unequal cycles would require a very eccentric orbit that somehow stays aligned with the "sun" -- which isn't happening. – Zeiss Ikon Jan 7 at 18:44
• Yes, as stated above, the effect of the second star would be minimal to any dark side of the planet since they would be on the antipodal position. Maybe (unsure of the orbital mechanics on this one) if the planet had a majorly skewed orbit by the gravitational pull of the companion star. this would make it that, even though the companion would be visible in the sky for half the year, its effects would be dramatically more apparent for only a short part of the "year." This would elongate the orbit and the true night may be a bit longer, with extended periods on twilight. – Sonvar Jan 8 at 0:36

If your planet has 1) a tilt and 2) a wobble (aka precession) with a period of exactly one year and in the same direction as the planet's revolution, then there will be locations in the "summer" hemisphere that are permanently daylight, locations in the "winter" hemisphere that are permanently night, and locations along lines of latitude in between that have whatever permanent day/night ratio you're looking for. If at one of those latitudes there happened to be a small solitary continent then that would effectively be the world you're looking for.

If a point on a planet had a 30 hour night, there would be a corresponding point on the opposite side with a 30 hour day. A planet wide day/night cycle as the one you desire is not possible.

You could extend the dark period with eclipses. The simplest would be to have a single large object eclipse the sun. Your "planet" would in this case be denominated as a moon. If the moon has a circular orbit, close to a large planet, it would be in the shadow close to 50% of the time. While not in the shadow, it would have a normal day/night cycle. If this is synchronized with every other orbit, you could have something like a night almost 3 times the length of the day.

You may have different results with an elliptical orbit, but I don't think your results will be much better.

The planet you are orbiting could itself be a moon. If the orbit around this parent planet is also correctly synchronized, you could further extend orbital times and eclipses in a huge, complicated and unlikely mess.

A combination of planets and moons could as such give any desired day/night cycle, but would need to be very carefully synchronized. Any error would result in day and night being more or less random.

[edit:] Any displacement of mass, such as a human moving around on the surface, would cause enough error in a carefully synchronized system to gradually throw the whole thing off.

Inside of a sphere

(I added a second answer, as this is a totally different kind of answer from my othe one)

Your "planet" could be on the inside of a rotating sphere with a relatively small opening, which lets in a beam of light when it is oriented towards the sun. This opening could be a long slit of sorts, which would allow every part of the "planet" (or the inside anyway) to experience daylight.

This daylight would not be uniformly distributed across the entire (inside) surface, and some parts would have longer periods of light than others. In particular, the areas nearer the slit might have longer light periods. It is worth noting that a uniform distribution of light is never the case with actual planets either.

A side effect of the light hitting the inside of the sphere, would be a secondary emission of light. Or a reflection, if you will. You would be able to see the parts that were currently lit in the "sky". The scattered light might also be enough that you could see the rest of the surface dimly. This would vary with the effective size of the opening, angles, etc.

If you wanted atmosphere in your world, there would need to be a large wall all around the opening, or the opening would have to be sealed, but let light through.

If you will accept an engineered system and some fudging on what is day and what is night I think I can do your system:

Central body: very large black hole.

Around it is your planet and farther out a star. They are in a resonance orbit and the planet's rotation is also in resonance (think Mercury.)

The planet's rotation period is 19 hours, the star and planet match up every 38 hours.

When the star is on the far side of the black hole you have night (although the accretion disk and the jets from the black hole will make this a fairly bright night). When the planet and star align half the planet gets day and half the planet gets night.

Note, however, that you more get the star going away rather than setting--the day/night transition is fuzzy.

Your planet will need a very powerful magnetic field to remain habitable in this environment--while most of the radiation from the black hole will be aimed away from the planet some particles will no doubt end up coming in it's direction.

Yes, but not in the sense of a traditional star. Keep in mind that (discounting refraction and gravitational curving of light), less than half the Earth has line of sight to the sun at any given time. A sufficiently pointlike orbiting space light of some sort (fusion powered?) could be positioned near enough to a planet such that the combined effect of it's orbit and the planet's rotation keeps it above the horizon only the desired fraction of the time. However, this would also lead to a large polar region that gets no "sunlight" at all.

(If anyone would care to do the math, feel free to edit; the orbital mechanics of this are eluding me at the moment)