201
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 ...
- 12.8k
189
votes
Accepted
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 ...
- 22.4k
130
votes
Accepted
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 ...
- 42.2k
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 ...
- 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 ...
- 11.7k
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 ...
- 26.6k
71
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 ...
- 117k
71
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 ...
- 1,722
64
votes
Accepted
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.
...
- 66.2k
60
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:
- 701
60
votes
Accepted
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 ...
- 23.4k
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 ...
- 276k
55
votes
Accepted
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 ...
- 41.7k
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 ...
- 20.2k
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. ...
- 117k
52
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 ...
- 39.5k
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 ...
- 99.8k
51
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....
- 42.2k
49
votes
Accepted
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 ...
- 136k
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-...
- 22.2k
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 ...
- 276k
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 ...
- 136k
46
votes
Accepted
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 ...
- 42.2k
45
votes
Accepted
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 ...
- 54.8k
45
votes
Can planetary bodies have a second axis of rotation?
I asked this same question, on the physics stack. The answer is that a body can have only one axis of rotation. Below pasted is the link to the question and the answer I picked.
https://physics....
- 304k
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 ...
- 910
44
votes
Accepted
In a world without stars, how would travelers navigate at night?
First off, this question reminds me of the Doctor Who episode The Pandorica Opens, in which the TARDIS exploding destroys all the stars.
To get on with the main question, there are four ways that ...
- 9,634
43
votes
How long will it take to discover they live on a moon and not on a planet?
Unless all the land mass on the tidally locked moon is on the side facing away from the gas giant, the humans will discover they're orbiting a gas giant during the stone age:
If the land mass is ...
- 1,678
43
votes
How could a spaceship, because of mechanical issues, crash-land on a planet they weren't intending on travelling to?
Failed slingshot maneuver
Space vehicles even now frequently use a gravity assist technique to gain velocity toward their target. The Galileo probe used 5 such maneuvers (2 around Earth) to get to ...
- 2,451
42
votes
How long would it take us to detect that the earth had been enclosed in a shell 1 light year in radius?
The answer depends entirely on the sophistication of the simulation.
The answer by AlexP suggests that the screen could be discovered in the 1600s or 1700s by parallax, but that's only true if the ...
- 1,425
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