193 votes

What would make scientists realize they were on a flat world?

Apart from the horizon topic that was already covered by Separatix and Ctouw, they could quickly verify their observation by measuring the angle towards the sun at different points of the planet at ...
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  • 12.4k
175 votes
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What would make scientists realize they were on a flat world?

Daybreak and nightfall would be spectacular A flat coin shape would have a day face and a night face with sudden transitions because unlike a sphere, it blocks all sunlight with its own shadow, there ...
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  • 21.7k
129 votes
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How could a planet have a sky without stars at night?

Dust cloud. The star may be residing in a dust cloud with no other stars nearby. This interstellar dust will create a faint nighttime glow, and can be thick enough that no other star's light can be ...
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  • 41.2k
83 votes

If Sweden was to magically float away, at what altitude would it be visible from the southern hemisphere?

Given Sweden has a latitude of 60° N and south Africa of a bit over 30° S, you can never see one from the other no matter how high one is and no matter how small the planet is (as long as it still is ...
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  • 1,111
78 votes

Would 'cheap' FTL make powerful telescopes obsolete?

1000 times the speed of light means you can visit something 500 lightyears away in a one-year round trip. 5000 lightyears would take a decade and you are still not even leaving our galaxy. In contrast ...
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  • 11.1k
73 votes

What would it feel like on the surface of a planet while it collides with another planet?

Virtually everything in Mindwin's answer is wrong. The slowest possible approach of the rogue to the earth would occur with a Hohmann transfer orbit, and in this case orbital energies dictate a ...
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70 votes

How could a planet have a sky without stars at night?

Perhaps their planet is on the inside of a giant Dyson sphere that was created by an ancient civilization. This would be a vast solid shell that surrounds their entire solar system, the inside of ...
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  • 1,702
68 votes

What would make scientists realize they were on a flat world?

Horizon effects would be the first signal. As a quick and dirty calculation, the distance to the horizon in miles is half your height in feet. Given their visual range is going to be far greater ...
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  • 114k
64 votes
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How would skeptics know that a single-engine plane could not destroy a falling meteor?

I’m going to address this as a general question about using airplanes to stop meteors, rather than the very plot specific way the question is worded. Nope. For one very simple reason: Speed. ...
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60 votes
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How would someone hide an asteroid in the void of space so only they could find it?

The primary way to hide something in space is to make it uninteresting. Start with a boring asteroid, made out of silicate rock rather than metals or organic compounds that are worth mining, orbiting ...
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  • 18.2k
60 votes

How could a planet have one hemisphere way warmer than the other without the planet being tidally locked?

Mount Kilimanjaro, despite being close to the Equator, has permanent glaciers on its top. This hints toward the solution to your problem: orography! While one hemisphere is mostly flat, with limited ...
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  • 242k
56 votes

Could a disaster kill all (human) life on Earth but leave astronauts in low orbit alive long enough to return?

Plenty. Asteroid A sufficiently violent impact at a time where the resulting debris doesn't intercept the stations orbits would wipe out life but leave people in orbit alive. Volcanic Winter ...
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  • 76.1k
55 votes
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What would the effect be on Earth if Mars disappeared?

Mass panic and fears of the apocalypse Physically? Nothing. There would be no readily discernable physical effect on the Earth or us, its inhabitants. Emotionally and psychologically though, that ...
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  • 39.7k
55 votes

Why didn't we detect that exoplanet before?

Your simple answer is that no one has got round to checking that star yet. There are perhaps 2 million stars within 500 light years, of which about 150,000 are G-class like our sun. Corot and Kepler ...
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  • 19.5k
54 votes
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Can I keep our universe, but without the speed limit (of light)?

Yes, you can! You could imagine a universe where physics is based on Galilean relativity instead of special relativity. I'll skip over the mathematical details (unless you're interested), but ...
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  • 1,388
54 votes

What would make scientists realize they were on a flat world?

An Edge Not sure why this has not been said, but when you go for a long enough walk and get to the perimeter of the disk planet, there is an edge. In the Truman Show, the edge looks like this:
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53 votes

If Sweden was to magically float away, at what altitude would it be visible from the southern hemisphere?

There is no atmospheric height any object of any size can be, perpendicular to the location of Sweden, that could be seen by anyone standing anywhere in South Africa. I don't need math to prove this. ...
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52 votes
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Is it physically possible for a planet to have seasons of different lengths?

Yes and no. This NASA page has a good summary of why we have seasons (emphasis mine): It is true that Earth’s orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is ...
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52 votes

How would an astronaut conclude he's on Earth, but 600 million years in the future?

Even with Moon and Mercury out, the rest of Solar system should still be recognizable. Venus, Mars, Jupiter, Saturn and the rest should still be on their orbits, though those orbits may shift a little....
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  • 41.2k
52 votes

Exactly how far apart are nearby stars from one another?

An exact answer The position of a star in space can be specified by three coordinates: Its right ascension, $\alpha$, its declination, $\delta$, which are collectively referred to as equatorial ...
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  • 97.5k
51 votes

What would the sky look like from the surface of a planet with rings?

Very cool, I'm sure. Roy Prol put together a fantastic animation describing what a Saturn-like ring system would look like from the surface of the Earth: What Earth Would Look Like With Rings Like ...
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51 votes

How could a planet have a sky without stars at night?

One possibility is for the surface of the planet to be covered in highly luminous matter. Perhaps all the surface is an interconnected network of bioluminescent life. There is no moon (assumed ...
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  • 37k
49 votes
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How can a planet have a deadly eclipse-like "spotlight"?

A wobbling pulsar will do the trick. Pulsars emit a lot of energy in narrow beams that come from their poles. The slowest ones flash every few seconds; make its tilt wobble so that it is not pointing ...
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49 votes

How could a planet have one hemisphere way warmer than the other without the planet being tidally locked?

Combine an significant axial tilt with a elliptical orbit. Axial tilt allows one hemisphere to be in winter while the other is in summer. Earth has approximately 23.44 degrees of tilt. Even in mid-...
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  • 20.9k
47 votes

Can a dedicated amateur astronomer spot a rogue asteroid?

The sky is too big to let only professional astronomers look at it. Consider that professional telescopes have limited time windows for specific researches. And if you want to spot potential hazards ...
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  • 242k
46 votes

What could make a planet more radioactive at night?

The ground worldwide might be rich in radioactive ores, but you have to dig at least half a mile down to find them. However, many plants have roots that do go that far down. Those plants are ...
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45 votes
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Could a disaster kill all (human) life on Earth but leave astronauts in low orbit alive long enough to return?

I would say none or close to none. The main problem is that being in space isn't very different from being in some confined places on Earth (with regard to isolation). For example submarines, some ...
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  • 1,344
45 votes
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Is a "long exposure"-like night sky possible?

Is there a (realistic) way for such a planet to exist? No. The minimum exposure time for such a photo is about 10 minutes (360 degrees in 24 hours means that to have 15-degree arcs you need one hour ...
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  • 52.3k
45 votes

In a world without stars, how would travelers navigate at night?

Well... I guess they would have to go by the other planets then, the Gegenschein could also help: Gegenschein (German: [ˈɡeːɡənʃaɪn]; lit. "countershine") is a faintly bright spot in the night sky ...
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  • 851
45 votes
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How would people detect a 1 year time jump between star systems?

Alpha Centauri is a multiple star system Particularly, its main components, Alpha Centauri A and Alpha Centauri B are orbiting each other with 80 years period. Assuming that wormhole jump was prepared ...
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