# How would people living in eternal day learn that stars exist?

In a world I am building, the day lasts longer than the year, 9 times longer in fact. The native people of this world have been forced to migrate around the world, both avoiding the scorching desert of noon and the freezing winter of night. This world is otherwise rather unremarkable on the surface. Outside of the planet is a ring as well as many small moons, so many that the tides are rather small and unpredictable, but as I was designing their culture I realized something, without seeing the stars, would the have astronomy?

How would a species that lives in eternal day have any knowledge of the stars?

• Comments are not for extended discussion; this conversation has been moved to chat. Dec 23, 2016 at 3:38
• Aside: I'm curious what your definition of "day" is in this world. You may want to investigate the difference between sundial time and mean solar time (clock time) en.wikipedia.org/wiki/Solar_time Dec 24, 2016 at 20:33
• that planet wouldn't support indigenous life. the side that face a sun for that long that is habitable to humans without the need for environmental suits would be fried and boil any water into the atmosphere where it superheated and create weird winds on the surface of most likely hurricane or tornado like winds nearly constantly. when the earth is finally gravity locked to the moon in 5 bil years, one earth revolution will take take 28 days but then the sun will supernova anyway, Dec 25, 2016 at 21:19
• @GAlexander the planet is not tidally locked as I clearly explained Dec 25, 2016 at 22:40
• @Tiny TrEs-2b you need to step back and off your high horse. Your entire sceneraio is lacking copious amounts actual science. A planet as you describe would probably be inside the radius of Mercury and friend to a crisp. Learn Kepler's laws. Gravity would not need be the cause for small tides in this scenario, take a course in graduate thermodynamics, atmospheric weather and ocean subduction. Dec 25, 2016 at 23:00

## The poles provide the ability to stay on either side safely.

Since the planet has a relatively small axial tilt (13 degrees), the North and South poles of this planet shouldn't be incredibly cold relative to the rest of the world.

They would be inhabited, just like the rest of the "belt" that spans the planet. Observers at the either pole could (somewhat) safely foray into the night area and back without being stranded in either condition (night or day), having the sunrise/sunset zone nearby. This could mean safe stargazing throughout an entire lifetime, and develop astronomy.

### Compared to other ideas

• This phenomena allows astronomy to develop at a constant rate, as opposed to allowing a few observations every time there is an eclipse (as other answers suggest).
• This also accounts for the danger posed by 4.5 years of constant sunlight or darkness by providing a means to switch to the other side. Comparatively, answers that suggest "people want to explore" do not account for the resulting deaths of those explorers when they cook or freeze, subsequently wasting all that they learned.
• Some answers suggest that the sunrise / sunset zone has enough clarity to see stars and planets, but all spectra recorded will be tainted with sunlight; you need "true night" to get accurate results and determine more about the stars.
• While traveling from base to base, as some answers suggest, may seem effective in practice, locating the same bases when given the entire hemisphere may be challenging - and bases will likely be damaged severely by frost or heat.
• I'm not sure that a small axial tilt prevents the poles from becoming cold; the sunlight still arrives at a steep angle, and that's the main factor affecting the polar temperature AFAIK. Do you have a reference? Dec 23, 2016 at 2:33
• @HarryJohnston While the poles should still be colder relative to the rest of the planet I'm reasoning that for a near-tidally locked world, the extra heat or cold produced by a greater tilt (such as Earth's) would render the poles uninhabitable. It could be worse. Dec 23, 2016 at 2:37
• Possibly relevant: en.wikipedia.org/wiki/Inuit_astronomy Dec 23, 2016 at 2:46
• Actually, a good part of the world may be habitable year-round, if you have good food storage ability and/or can live on a diet of mostly sea life. See this simulation of 50 years of tidal lock on Earth: meteo.mcgill.ca/~tmerlis/coupled_tidally_locked.html It appears that atmosphere and oceans transmit heat from dayside to nightside well enough that the planet remains mostly habitable. The problem with surviving 4 1/2 years of night would be food supply, not cold - which would be no worse than Arctic peoples on Earth were able to survive with very limited technology. Dec 23, 2016 at 3:28
• Earth's polar regions remain habitable (though extremely uncomfortable!) even after six months of constant sunlight. Dec 23, 2016 at 20:54

# People are curious

Humans, at least, are very curious. Shamans on spirit journeys, young men on adventures, and outcast groups in exile might all end up traveling into the night zone for one reason or another. And if they had not seen stars before, they would be amazed, and behold them with wonder.

Once word got out of these stars, many of the religious or scientifically minded would want to go check them out.

• How many of those adventurers make it back out of the night zone after having gone deep enough to see the stars??? I would expect the environment to be quite lethal before it became dark enough for astronomy. Dec 20, 2016 at 23:50
• @LorenPechtel you don't necessarily have to go deep to see the brightest stars, or other planets. Dec 21, 2016 at 11:06
• @LorenPechtel The top of Mount Everest is hostile to human life. Why did people go there? Famously, "Because it is there." Dec 21, 2016 at 13:00
• @LorenPechtel people spend literally months in freaking space. You can't get any more hostile than almost vacuum. Dec 23, 2016 at 0:34
• The Night Zone would not be that bad, most likely. A habitable planet would presumably have atmosphere and oceans, which redistribute heat. So the night side shouldn't get utterly cold -- and the Inuit were able to survive at latitudes where the polar night lasts several months even before modern technology. Also, one wouldn't have to go all the way into the deepest night to learn that stars exist - the few brightest can be seen in twilight. Dec 23, 2016 at 3:12

If they're avoiding both the heat of the day and the cold of the night then there are dawn and dusk people.

Most likely you have four main groups, two who move constantly and two who move and settle for long periods.

The dawn tribe will move until they start seeing stars, then it's time to settle until the heat of the day catches up with them.

The evening tribe will move when the first stars of the evening start showing as the signal that the temperature is going to drop.

Both these groups will overhaul the constantly slow moving tribes in their sectors when they move and those who move further ahead at dawn or stay later in the evening will tell stories of the heavens lighting up with stars at the extreme of the survivable temperatures.

• Brings new meaning to "morning person" Dec 20, 2016 at 23:23

### Total Eclipse

I know this isn't directly an answer to your question, but the novelette Nightfall by Isaac Asimov deals with a civilization living on a planet in a system with six suns which keep the whole planet continuously illuminated. The people have no actual awareness of any stars beyond their local solar system, as they cannot see them and they are too distant to detect their gravitational influence.

Every 2050 years, another planet in the system coincides with the positions of the six suns and the civilization's world such that, for one brief interval of a few hours, for one side of the world 5 of the suns are "set" and the sixth is eclipsed by the other planet. For those few hours, a world that has always known daylight is plunged into darkness.

The story goes on to describe the catastrophic effect that one brief night has on the civilization—and indeed has had on every civilization that world has brought forth in its past as well. It's a good read.

But the mechanism of a global nightfall caused by an eclipse would provide a means for the people in your world to learn that other stars exist. (And the story may give you some ideas about how that people might react in the face of that discovery.)

Link to complete short story: https://www.uni.edu/morgans/astro/course/nightfall.pdf Was later made into a novel of the same name.

• IIRC Kalgash II isn't a planet; it's a moon. But I also recall it being about the same mass as Kalgash, so that could be wrong.
– HTNW
Dec 21, 2016 at 0:48
• I would find it hard to believe that people in this world would react so strongly to darkness given that they can still see it if they lag too much behind the sunset or overtake the sunrise by too much, which is bound to happen. Dec 22, 2016 at 1:43
• Rad the short story "nightfall", which the novel was based on. IMO its much sharper and direct for being short. Dec 24, 2016 at 19:10

## Visual Discovery in Dark Areas

If your scenario allows for people to venture into dark areas where stars are visible to the naked eye, then certainly that will be the easiest way for people to discover stars.

## Non-Visible Light Astronomy

If your scenario requires people to stay in areas where stars are not visible to the naked eye, then techniques other than visible-light astronomy will need to be used. I'm not sure if all wavelengths in the electromagnetic spectrum have star detecting applications, but many do:

(Source)

Gravitational fields are also means of detecting stars.

## Problems of Developing Technology in Nomadic Cultures

Depending on how much time they are required to keep moving to avoid the noons and nights, they might not be able to develop enough technology to reach modern Earth's levels of technology. So many factors of modern technology have evolved in stationary workshops, where large, heavy, non-mobile things like a blacksmith's forge or a steel foundary's massive smelting apparatus can be built, maintained and operated.

Metalurgy and other technological fundamentals might be difficult to develop in a very actively nomadic culture. For example, if the days last for 9 years, but the planet is millions of miles wide, they may be required to move extremely rapidly all the time to stay safe from the noons and nights. If the planet is only the size of our moon, though, they could stay in one place for many earth years on end before having to move to a safer location, giving them time to build shops in which to develop non-mobile technologies (like Very Large Array telescopes.) If they do have enough time to build shops, but later have to move on, if they aim to, they can eventually come back to their shops when they have gone all the way around their planet. This would allow them to use stationary technology, just at a different pace and style from the way it developed on Earth.

So, the size of their planet will play a huge role in shaping their development of non-visible light astronomy technology.

• But the parent star is just another star and due to the closeness would overwhelm any detector, even in the non-visible spectrum, wouldn’t it? You’d have to watch for other stars in the parts of the spectrum where the parent star doesn’t emit, but other stars do. Dec 20, 2016 at 17:58
• It's a good answer, except there has to be a very compelling reason why they would build non-optical telescopes to view something they have never seen. It's compounded by the task being, as you point out, very difficult to do even with good reason. Dec 20, 2016 at 18:24
• @Michael Yes, that is how they would need to proceed. Dec 20, 2016 at 18:33
• @Samuel Yes, astronomy dealing with non-daily necessities is definitely a thing that would most likely only develop after society had developed enough technology to meet it's daily needs, and that could take some time. Cavemen certainly didn't develop radio telescopes. Dec 20, 2016 at 18:35
• @Samuel, in real life cosmic microwave background radiation was discovered accidentally while working on radio antennae. Radio itself was used for communication before it was used for astronomy. And, if I may flag up my own answer, some astronomical objects can be seen daylight by the naked eye, so astronomy would have a reason to get started. Dec 20, 2016 at 19:28

In addition to the three good answers so far received, the people of your planet would almost certainly be able to see certain astronomical objects by daylight. On Earth even in daytime we can regularly see with the naked eye the moon, obviously, plus several planets, some meteors and comets, and supernovae when they occur.

It is true that one cannot normally see stars in daylight from Earth except during a solar eclipse. The moons of your world are small, so a situation like an Earthly solar eclipse, when the shadow of a moon apparently blacks out the sun entirely, will presumably never occur. Nonetheless you might get partial darkening when a moon passed between your planet and the sun, enough to see a particularly bright star. Your world might simply have brighter and/or nearer stars in its sky so that keen-eyed people can spot them when conditions are good.

In any case, given that your planet's people will be able to see some astronomical objects there is no reason why the science of astronomy should not get started. Telescopes have many other uses than astronomy so would most likely be invented anyway.

The brave and curious will make special expeditions to the night side of the planet as suggested in previous answers. In fact astronomy is not the only reason why they might want to visit the night side - doing so could bring them advantage in war, if, for instance, they wanted to launch a surprise attack from an unexpected direction. Trade expeditions might wish to take the shortest route possible even if it did mean wrapping up warm. People might simply wish to check up on their property, to which they intend to return the next day. Criminals and refugees might flee their pursuers to the twilight zone where survival is less difficult than in areas of full night. These travellers through the night and twilight zones will be intrigued to see that unlike the familiar celestial objects these other lights appear to hold their places in the sky. There might be religious pilgrimages to see this wonder.

Build a telescope.

A decent telescope can see stars even during the day. For a people dependent on crossing more or less unfamiliar ground all the time being able to see far ahead would be of tremendous value so telescopes would be built and refined if they have the technology to make them at all.

• plus of course you can see planets during the day with the naked eye.
– John
Dec 20, 2016 at 20:03
• Why would you build a telescope if you were not looking to see stars? I think you would only build a telescope and aim it at the sky if you were looking for things (stars). Dec 21, 2016 at 1:30
• @EricJohnson they would build a telescope to look at the rings and moons, and then notice the stars by accident.
– IMil
Dec 21, 2016 at 7:50
• @EricJohnson To see objects in the distance? Not stars, but enemy armies, islands on the see, passages on mountains... stuff like that. And if they already have some decent telescopes, what would stop them to turn them towards the sky out of plain, pointless curiosity? Dec 21, 2016 at 12:41

This is not a truly nomadic culture as they are able to follow the same route over and over. Assuming adequate cooperation between the sunrise population and the sunset population they can become not quite so nomadic.

In their spare time they can build structures of use a bit at a time. They will have to move on before it's done (there's no point in such construction unless it's going to be good for centuries) but in time they will come back to it. Once they have weather-protected storage they can build spare tools and leave them behind--this reduces the amount of material they must lug and thus frees up time. More tools, an easier life. Eventually you will have a society where instead of eternally trudging around the planet they move from base to base, traveling very light between the bases and with a very good road connecting these bases.

Now we are able to start playing with science. In time they will develop photography--and just because people can't survive the extremes doesn't mean a camera can't.

Progress will be exceedingly slow but it will happen.

It seems reasonable that the near edge of the night zone won't be too hostile for several days and it is also fairly likely that people might end up there because of delays or accidents.

Equally as mentioned in another answer humans have a very long history of venturing into hostile environments. After all there is quite a bit of tourism to the arctic to see the northern lights so it's not a big stretch to imagine that people might linger in the night zone for a while just to see the stars.

Once you get any sort of scientific culture established it is entirely plausible that scientist might set up bases to venture into the 'deep night', for comparison just consider the expeditions of people like Shackleton, Scott, Amundson ect to the poles all of which were extremely arduous and dangerous. Indeed in this case you don't even have to go anywhere just wait for the night to catch up so building a well stocked base isn't that unfeasible.

As well as curiosity there could be economic motivations, perhaps there are animals which live in the night zone which are sought out by hunters for fur, meat or fat, indeed in this world ice could well be a valuable commodity, as indeed it was before the advent of refrigeration.

A low-density atmosphere and a solar eclipse

The sky brightness may be strongly reduced with an atmosphere of low density and/or fewer molecules and dust that disperse light. For instance, removing a bunch of nitrogen and ozone could strongly reduce the sky brightness.

A solar eclipse could further reduce it to levels where stars become visible.

Why not? Bear in mind that sometimes we can see our moon during the day. If the celestial objects are big enough, close enough and reflective enough, at the right angle they can be seen even in broad daylight. It's just a matter of size and brightness. So these people probably would've seen some of these objects, or even part of the ring. Their curiosity for the sky would take flight from there.

Brave and foolhardy early explorers, doomed though they were, may have managed to communicate images of, and/or comments on, what they saw in the Shadow Zone before they froze. Perhaps they managed to send images, or even stream movies, via wireless communication technology. Perhaps they left material behind on some sort of storage media. Even hand drawings and writings would be enough to establish that there's Something Up There. I'm assuming each sub-culture or tribe will have established markers around the planet, its own Road or Path or Belt to help them re-visit the same useful places on every Go-Round. So it's not inconceivable that such artifacts would be picked up again.

Subsequent to that initial discovery, how it plays out will depend on the level of technology. To me the idea that this society has access to advanced technology is only a slightly bigger stretch than the idea that they've survived at all (due to factors that others have mentioned here). Perhaps they're relics of long-ago stranded space-farers? Whatever the history, if they have some reasonably advanced technology, then this might include the wherewithal to set up unmanned observation stations in the Death Zones. Or perhaps insulated, heat-shielded, climate-controlled bubbles that would allow people to actually live there, much like our own Antarctic researchers or conceivable near-future colonists of the moon or Mars.

Even at a lower tech level, localized quirks of geology might make survival possible: a deep enough hole in the ground might insulate you from the big scorch, and various geothermal features might provide enough heat to help you survive the big freeze (even, in some places, close enough to the surface to allow for star-gazing).

Do these people have basic electrical technology? If so, they could build a radio telescope. Radio telescopes work just fine during the day because radio waves aren't diffused by the atmosphere as much as visible light is. You could see the stars with a radio telescope the same way you can see the stars when you're in outer space. (Speaking of which, they could see the stars for themselves if they built a spaceship.)

They may also be able to see the stars if their local astronomical neighborhood was more crowded than ours. Multiply the brightness of our brightest star by ten times and it'll be visible during the day. This could have happened if the stars in our neighborhood were a little closer or a little brighter. The same goes for planets. Comets are already sometimes visible during the day, though this is a bit off-topic.

If you go down a well, even in full day light you can see the stars... that's how one of the early Greeks realised the stars were there in the day, hidden behind the bright sunlight.