10
$\begingroup$

Premise

I envisage a world of would-be navigators with roughly Bronze Age technology, sailing on ships to explore their planet. In contrast to our history of navigation where we "cracked the code" around the dawn of our Bronze Age, I want the narrative of sea navigation on this world to be as arduous as possible. Instead of simply blanketing the sky with an opaque atmosphere to obscure the stars outright, I would like the stars to move around the sky in an erratic and baffling manner. This way there is a visceral conflict with the emergence of intellect on this world. In other words, although the would-be navigators have the intellect to gather materials for building ships and have knowledge of the engineering that is required to make them sea-worthy, I want the failure to understand celestial navigation to bring the celebration of their thus far potent intellect to a halt. The chaotic, incomprehensible movement of the stars overhead would serve as the ultimate mockery -- which is the goal.

We can assume they can navigate to some degree, as even the most inept captain can hug the coast lines and record wind patterns. However this world has vast oceans. A lucky few who have sailed there and back by sheer luck speak of entire continents. These continents are far beyond the horizon, where the vast majority of the expeditions became lost or crashed and never heard from again. Society has since shunned those who claim they went beyond the horizon and back. And most importantly, nobody even looks up to the sky at night for navigation. The stars serve as just a form of recreation; they are gazed at by the sailors before they sleep. Those who have tried to navigate by them have long since given up or gone completely insane.

This is the situation on the ground in this world. Now we might think to ourselves, we have other Bronze Age tricks up our sleeves, but such ideas have not dawned on these people yet.

Question

Navigation has many forms, but the scope of this question is restricted to solely that of celestial navigation. That being said, which part of the universe would make celestial navigation the most difficult for an Earth-like (tilt, rotation, ect) planet of potential navigators? The answer can be an example in our actual universe, or a theoretical galaxy -- as long as it still has plausible astrophysics behind it.

I would like to confirm there is such a place somewhere in the universe so that my premise has a sound foundation.

Quality Metric: The more non-stationary the stars appear, the better. This can be achieved either via chaotic disturbances in the stars location in space or the speed a star moves.

Planet Details

  • Planet Size: larger than Earth, a Super-Earth
  • Rotation: Earth-like
  • Moon: Earth-like
  • Tilt: Earth-like
  • Astronomical Position: ??? (this is what we need)
$\endgroup$
10
$\begingroup$

This is not the first time intelligent life has arisen on this planet.

Your planet orbits an intergalactic star: normally, the sky would be pitch black at night, with only the faintest dots of distant galaxies visible. But instead, the sky is criss-crossed with moving stars, stars that flit quickly across the sky scape. Why?

They're satellites and space stations, left over from the previous time intelligent life evolved on the planet. To make things really convenient, perhaps they are even currently occupied: the planet became toxic to its occupants, and they fled for the climate-controlle safety of their orbital stations.

In our night sky, the ISS can appear as bright, or brighter than Venus, so luminescence isn't a problem. As you can see here satellites orbit in every possible arrangement and direction. Some of these 'stars' would take just a few minutes to completely cross the sky.

$\endgroup$
  • 2
    $\begingroup$ Possibly... but we humans never used Venus to navigate. We used the bright stars and constellations with fixed positions. Having a bunch of non-fixed objects zipping around wouldn't create a problem for celestial navigation. $\endgroup$ – HopelessN00b Aug 12 '18 at 1:52
  • 2
    $\begingroup$ See my first sentence: the planet is in intergalactic space. There would be no stars except the artificial satellites. $\endgroup$ – Daniel B Aug 12 '18 at 2:50
  • 3
    $\begingroup$ That’s not how intergalactic space works. The fixed points of light in the night sky would be galaxies, rather than individual stars, so you haven’t actually solved that problem. Novel try, though. $\endgroup$ – HopelessN00b Aug 12 '18 at 4:18
  • 2
    $\begingroup$ Nah. Stick the system in the middle of, say, the Boötes Void, and you're 125 million light years from the nearest galaxy. We're fifty times closer, and can barely see it with the naked eye. Until they have telescopes, they'll have no idea other galaxies even exist. $\endgroup$ – Daniel B Aug 12 '18 at 4:40
  • 3
    $\begingroup$ DanielB, The Bootes Void contains galaxies - about 60 are known. That means that the nearest galaxy to a given galaxy should be, on average, about 68 million light-years away. It's believed that there are 2000 galaxies in the void, making the mean separation of 10-20 million light-years - only a few times as far as Andromeda is from the Milky Way (2.5 million light-years). The civilization might very well know know that other galaxies exist. I think @HopelessN00b might be right. (1/2) $\endgroup$ – HDE 226868 Aug 12 '18 at 13:16
8
$\begingroup$

Let's spin that sucker so fast you literally don't have time to take bearings

You need an Earth-like planet, but how Earth-like?

As we learn more about exoplanets, we find that some rotate very fast and others orbit very fast.1 We don't know yet if such fast rotation and orbits can support life (although we are learning that it might be a big deal), but let's assume that one can. The stars are screaming through the sky so fast sundown-to-sunup, and the constellations changing so fast spring-to-fall, that you simply can't keep track of them well enough to navigate.

And just to add insult to injury, let's put the planet near the galactic core

Yes, too close to the core and you're yesterday's microwave dinner. But, let's get close enough that your inhabitants have evolved to withstand a bit higher than we expect radiation — and have so many stars in the sky that are so close together that it's literally difficult to distinguish one star from another.

If they were standing still!

The combination of high star density, high rotational speed, and high orbital speed would make bronze-age navigation (and likely navigation up through the 1700s) nearly impossible.

and, as an alternative...

On a completely different note, you could take a good old fashioned solar system, something a lot like Earth, and add so many comets and a nearby asteroid belt that the sky at night is in nearly constant motion.

Edit: Solar rings

One more idea. In a now-deleted answer to this question,2 WillK described the star Formalhault, which has a solar ring kept in place with inner and outer shepherding planets. If your habitable planet were the inner shepherd and the solar ring was thick and not too distant, then your night sky would be alive with "stars" that were never in the same place twice.


1That fast-orbit link is for a planet with an 8.5 hour year. Please keep your hands and feet inside the ride at all times.

2This was a brilliant answer, but Will misunderstood the question. I understand why it's deleted, but it's a pity there are those without the rep to see the answer. It's worth the reference.

$\endgroup$
  • 4
    $\begingroup$ Upvote For planet with eight hour year. Holy shit $\endgroup$ – Daniel B Aug 11 '18 at 18:25
  • $\begingroup$ @DanielB Yeah, I'm only about 17520 years old. $\endgroup$ – tox123 Aug 12 '18 at 0:49
  • $\begingroup$ Spin that fast and the winds would be too high to safely sail (and wildfires would rage out of control). Near the galactic core, radiation would be so intense that life (beyond maybe some multicellular life near hydrothermal vents) can't form. And lots of comets and asteroids within visual range means a lot more impacts (and thus a lot more life-erasing impacts). $\endgroup$ – RonJohn Aug 12 '18 at 2:19
  • $\begingroup$ Oh, @RonJohn, you're having no fun with this question at all! And I wonder. I didn't say they were at the core, I said they were near the core. How close need you bee before the sky is ablaze with light? The spinning might cause storms like you say, or might not. Eventually the air spins up to the speed of the planet (unless space is causing friction). And we have no proof yet that shepherding planets of a solar ring experience any of the impacts you suggest. Nope. No fun at all. $\endgroup$ – JBH Aug 12 '18 at 3:47
  • 2
    $\begingroup$ Grumpy cat is too cheerful! $\endgroup$ – RonJohn Aug 12 '18 at 3:59
5
$\begingroup$

A swiss cheese-style dark nebula

Celestial navigation requires seeing other objects in the sky. But you can't do much of that if you can't see many celestial bodies. Therefore, you need to place your planet somewhere where it will be enshrouded in gas and dust. The solution is a nebula of some sort. A dark nebula is an extraordinarily dense nebula that blots out most things behind it or outside it; it would be the perfect choice if you want to be able to see very few objects.

Now, here's the thing: You still want some stars to appear in the sky, right? But you care about how the stars appear to move, not how they actually move in three-dimensional space. Therefore, I'll still suggest a dark nebula, but one that has holes in it, kind of like a gaseous block of swiss cheese. From time to time, stars appear in those holes, but as the gas moves and churns, holes open and close, and it seems like the stars appear and disappear, at random times. It becomes nearly impossible to track any single star.

To create the necessary turbulence on short timescales, perhaps . . .

  1. The planet could be near the edge of the nebula.
  2. The nebula could be colliding with another gas clouds.
  3. The nebula could have stars embedded in it, which would cause turbulence via radiation pressure from their light.

Barnard 68 is a classic example of a dark nebula, opaque at visible wavelengths but optically thin at infrared wavelengths:

Barnard 68
Image credit: European Southern Observatory, under the Creative Commons Attribution 4.0 International license.

Why true stellar motions won't work

A seemingly obvious alternative is just an area where stars move very quickly, or appear to. This usually requires an extremely massive object, like a black hole. We recently saw a star, S2, pass close to Sagittarius A*, the supermassive black hole at the center of the galaxy. It traveled at about 7650 km/s at its closest approach.

We can calculate the apparent proper motion of the star in the sky using the formula $$\mu_{\theta}=\left(\frac{v_{\theta}}{4.74\text{ km s}^{-1}}\right)\left(\frac{d}{\text{parsec}}\right)^{-1}\text{ arcsec yr}^{-1}$$ where $d$ is the distance to the star and $v_{\theta}$ is the component of the star's velocity perpendicular to the line of sight. At $d=1\text{ pc}$, S2 could have had a proper motion of 1614 arcseconds per year, which is . . . not a lot.

This would certainly be noticeable, but it would be easy enough to account for. Plus, it would require your planet to be close to the black hole. Which isn't great.

$\endgroup$
  • $\begingroup$ "as the gas moves and churns, holes open and close"... on the timescale of a human life, or even a few centuries? That's ... a very very very fast moving nebula. $\endgroup$ – AlexP Aug 11 '18 at 17:01
  • $\begingroup$ @AlexP Placing the planet near the outside might be a solution to that, or in an area populated by massive stars. The radiation pressure from those stars could cause turbulence that would influence the motion of the gas. $\endgroup$ – HDE 226868 Aug 11 '18 at 17:04
  • $\begingroup$ Will the cloud actually stay a dark cloud if the planet's star is inside it? $\endgroup$ – Paŭlo Ebermann Aug 12 '18 at 7:20
  • $\begingroup$ @PaŭloEbermann I'm reasonably certain it would be. While hot, luminous stars can ionize nebulae, causing further emission from the surrounding gas and the eventual dissipation of the clouds, dimmer, cooler stars with weaker stellar winds would contribute negligible amounts. For instance, Epsilon Ori ionizes the gas around it to create a reflection nebula, but the Sun - a few hundred thousand times dimmer - couldn't do the same, in the same environment, over short timescales. (1/2) $\endgroup$ – HDE 226868 Aug 12 '18 at 13:03
  • $\begingroup$ Radiation pressure is proportional to the luminosity of the source star; therefore, a solar analog would contribute a radiation pressure a few hundred thousand times weaker than a hot star, and a red dwarf - perhaps a couple orders of magnitude dimmer - would have an even smaller effect. (2/2) $\endgroup$ – HDE 226868 Aug 12 '18 at 13:05
3
$\begingroup$

I have a problem with your premise .. the earlist navigators, and arguably the best on earth were the Polynesians in the Pacific. They of course used the stars, but more used the knowledge accumulated over centuries of riding the waves, and currents, and using the wind to push their boats to know pathways between the islands they lived on. They had to do this to survive .. without accurate predictions about the movements of the fish they lived off of, and the ability to reliably bring food home from where it was caught, they would die. Then there is the whole thing about keeping out of the way of dangerous weather and climate things .. tsunamis etc.

These are people that learned the oceans by moving onto them from living onshore .. so navigation started from living according to temporal patterns in weather, sun and moon, and stars, on land. Careful observation gave them the information about currents, wind patterns and so on .. relating all that to the motion of the stars would be natural. The ones that do not move become reference points against which motion of the others is measured.

Now to relate this to your question .. No matter what is happening in the skys above them if they process visually in a way similar to us they will notice patterns in the sky. There will be some objects that do not move relative to the planent .. or at least there would be objects orbiting the same sun that will have simple relative motions ..

Alternative 1 So no matter what is going on outside the solar system there will be some stable references that can be a basis for navigation

Alternative 2 Human visual cortexes do a smashing job of picking patterns out of noise so (theoretically) there will always be something to use as a basis for predicting weather, movements of food sources and getting around to visit the relatives who live on other islands.

Either way .. my answer is that there will always be a basis for celestial navigatin no matter what is going on in the night sky. It is required for survival.

$\endgroup$
3
$\begingroup$

It's an interesting puzzle, and some good answers already.

The thing to keep in mind is that stars are pretty much fixed in the sky at least on a human lifespan. Stars do move around somewhat, based on their proper motion (very slow) and Earth's axial procession (25,700 year cycle, give or take). Neither happens fast enough for what you're looking to do.

With sufficient gravitational interaction, you could increase the planet's wobble. See this about Pluto's moons or Youtube video.

Saturn's Moon Hyperion undergoes a similar shift. In both cases, what you need is two large gravitational bodies tugging on your planet. The planet can either orbit a binary system, keep in mind, it would need to be a somewhat distant orbit to be stable and that would be iffy.

Or, your planet could orbit between two large bodies. The planet that comes closest to that situation in our solar system is Mars, which is tugged on by Jupiter as it orbits the sun. Mars, while it's axis is prone to large shifts, it doesn't happen fast enough for what you describe.

You mention a super-earth. A faster rotation and larger equatorial bulge and perhaps, I would think, a less flat solar system could all assist a faster planetary wobble, which is what you'd need.

A planet trapped in a Jupiter Trojan or Hilda orbit might experience sufficient wobbles, maybe. A large enough mass could coalesce but still be prone to significant wobbles. I can't do the math on precisely how fast those wobbles might be, but that might be your best option.

It might be possible, however, to observe the direction the sun rises in combination with the stars and work something out. The details get a little bit tricky at my pay grade.

I like the near the galactic core idea or the very short year too, but since those were already mentioned, no need to mention them again. You could also do some combination of the above.

$\endgroup$
1
$\begingroup$

Few visible stars, /large/ numbers of artificial satellites for an unknown reason.

You're not really going to be able to do this unless the stars aren't really stars. If the stars are moving around fast enough to be effectively unpredictable, and we're talking about a star density similar to that of around the Sun, then either something is moving the stars around at superluminal velocities, something is messing with the path of the light that's coming from the stars, or the stars are actually much closer objects masquerading as stars.

Of the three, the last is probably going to be the easiest to pull off without invoking some crazy physics, but you'd still need to explain who decided to put these satellites there, and if they're going to be behaving /truly/ unpredictably, they're also going to need to be able to change their orbits under power, frequently. Perhaps someone is doing a long-term intensive survey of everything going on on the surface of your planet with extremely high technology?

To get rid of nearby stars, have the system have been thrown out of its parent galaxy billions of years ago. Once it's sufficiently distant (say, Andromeda distance), it could be fairly discreet against the night sky, especially if the galaxy was a spiral one, and the star was thrown out in the plane of its disc.

$\endgroup$
1
$\begingroup$

Movements of planets and other celestial objects are repetitive, therefore predictable with sufficient observation.

To disturb this the light coming from the stars needs to be disrupted or distorted.

The planet can't have a moon, it could be used for navigation.

The sun can also be used for navigation.

A)

The planets atmosphere may have turbulent but very distinct layers of hot and cold air with high temperature differences.

It is conceivable that the resulting mirages and fata morganas combined with heat haze make it hard to distinguish stars and their position.

There needs to be very high atmospheric refraction and random turbulence in order for this to work otherwise the stars would simply dance around a comparably small spot in the sky.

Heavy solar activity like winds and flares, volcanic activity, vast deserts may possibly cause these things.

Mirages and fata morganas are usually close to surface level and I'm unsure if these would appear looking upwards.

B)

Two or more extremely heavy celestial bodies like black holes causing gravitational lensing with irregular orbits between the stars and the planet may heavily distort the night sky.

They need to have some sorts of random bursts of gravitation or their motion could still be understood and predicted.

$\endgroup$
1
$\begingroup$

Your planet is part of a rogue stellar system, detached from a galaxy. For sheer luck, the system is moving right in the middle of the Boötes void

The Boötes void (or the Great Void) is an enormous, approximately spherically-shaped region of space, containing very few galaxies. It is located in the vicinity of the constellation Boötes, hence its name.

At nearly 330 million light-years in diameter (approximately 0.27% of the diameter of the observable Universe), or nearly 236,000 $Mpc^3$ in volume, the Boötes void is one of the largest-known voids in the Universe, and is referred to as a supervoid.

According to astronomer Greg Aldering, the scale of the void is such that "If the Milky Way had been in the center of the Boötes void, we wouldn't have known there were other galaxies until the 1960s."

Your sailors, better, whoever lives on that planet, would have just a pitch black sky, with at most the view of the other planets of the system. No North Star, nothing at all to give a reference.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.