94
votes
Accepted
Why would space fleets be aligned?
The crews have evolved on worlds with orientation, so their psychology and conventions reflect the reality that they are planetary creatures.
Orson Scott Card captured the importance of orientation ...
- 9,732
65
votes
Killing a star safely
Problem: even if you could just stick a blanket over the sun, it is probably already too late. The solar system formed more than 4 billion years ago, and for all that time anyone who was watching and ...
- 72.7k
64
votes
Accepted
Is stealing the moon actually possible?
Plans for stealing the moon.
Shrink it
Well, this seems like the obvious solution. Just invent a shrink ray, zap the moon so it becomes the size of a basketball, then carry it home with you and ...
- 29k
45
votes
Alternate universe where life is more common; is it feasible?
Feasible
Can I have a universe with X?
Yes you can! If anyone tells you otherwise, tell them their argument fails because they are using the logic of this universe. Your other universe has different ...
- 65.6k
43
votes
Could gravitational lensing be used to protect a spaceship from a laser?
There are several problems with this.
First of all, when someone fires a laser at you, you aren't going to know it until it hits you, so this would only work if Ship A were CONTINUOUSLY creating a ...
- 16.9k
38
votes
Accepted
How much damage would a cupful of neutron star matter do to the Earth?
This is more or less my best guess.
We're talking about a mass of about one hundred billion tons, composed of neutrons, previously held together by a terrifying gravitational field - and now ...
- 55k
37
votes
Accepted
A planet illuminated by a black hole?
This scenario is quite problematic for two main reasons: evaporation and peak wavelength.
The black hole's lifetime is too short
We can make a rough estimate of the properties of the Hawking radiation ...
- 99.8k
35
votes
Is stealing the moon actually possible?
It's perfectly easy to steal the moon.
Just register a claim on it in every country and start issuing legal notices. It's been done before: Spanish woman claims ownership of the sun
- 12k
35
votes
A 1 kilometre wide sphere of U-235 appears in an orbit around our planet. What happens?
Normally, only the innermost kilogram of uranium in an implosion-type bomb actually undergoes fission (and only 0.6 to about 5g of mass are ultimately converted to energy - the sources don't agree on ...
- 55k
34
votes
Accepted
Black hole at the center of the planet
Your planet needs to be about 722500 times more massive than Earth for its core to undergo collapse into a black hole.
Leaving aside the small detail that at this point your "planet" would ...
- 8,779
33
votes
How can solar sailed ships be protected from space debris?
Generously spread the sail surface with self repair nanobots.
Any impact with dust or sub-dust size object (which is more likely to happen) will pierce a hole through the sail (and leave a cloud of ...
- 277k
32
votes
Accepted
What elements are useful for humans, but rare in our galaxy?
People need boron, because plants need boron.
https://en.wikipedia.org/wiki/Boron
Boron is a chemical element with the symbol B and atomic number 5.
Produced entirely by cosmic ray spallation and ...
- 304k
32
votes
Accepted
Making A Geosynchronous Orbit Impossible
Easy: Put a moon right above geostationary orbit.
If you have a 24h day, and a moon that takes 25h to circle the planet, any satellite orbit at geostationary height would be totally unstable. The ...
32
votes
What are the repercussions of two asteroids in the asteroid belt colliding?
Probably nothing
Robert Rapplean's answer is correct (upvoted) that without further information it is not possible to guess at an answer without more information, but there are some additional factors ...
- 25.8k
31
votes
Why would space fleets be aligned?
In our world
When you watch a movie, the ships are usually aligned. This is because of reasons that are most likely not based on our experience in space battle. I'm pretty sure I read about this and I ...
- 4,554
30
votes
How much damage would a cupful of neutron star matter do to the Earth?
The answer isn't entirely clear what the final state of the Neutron Star matter would be, but it would most definitely completely destroy the "Totally Normal Office Building", and most of the country.....
- 5,578
29
votes
How can solar sailed ships be protected from space debris?
A tiny piece of space debris is dangerous to the ship, as it may hit people, mechanisms, or fuel. But the damage to the hull itself would be negligible. It could simply be patched. The hull is the ...
- 25.3k
29
votes
If Earth had a smaller radius, but was rotating at the same speed, would its day be shorter?
The length of the day is strictly a function of the time earth takes to rotate. If your planet takes 24 hours to rotate then regardless of its radius, it will have a 24 hour day.
You can develop an ...
- 21.3k
29
votes
Accepted
Practicality of building a space station in the tail of a comet
The station is anchored to the comet
A comet's tail orients away from the star, and its size and properties change based on how close it is to the star. Because of a comet's elliptical orbit, there ...
- 87.8k
27
votes
Accepted
Could the moon crash into the earth if we colonised it and increased its mass?
As mentioned in comments, I don't have the full stability answer to hand (although see edit below). But I do have a practical answer.
The practical answer is that no feasible human effort could ...
- 2,141
27
votes
Accepted
How massive would a planet need to be to sustain negligible damage from impact with the Earth?
That really depends on what you consider 'negligible'. Is it 'Sterilization of all life, but planet is still there in one piece in the same orbit'? Or is it 'Everyone in the direct impact zone gets ...
- 4,270
27
votes
Black hole at the center of the planet
No
A natural occurring black hole that comes into existence due to mass collapsing onto itself must have more mass than the Tolman–Oppenheimer–Volkoff limit, which has been estimated to be around 2.17 ...
- 136k
27
votes
Earth is accelerated out of the solar system - do we keep the Moon?
You're going to lose the Moon.
At the Moon's current distance, the Earth's gravity can only change its velocity by $0.002m/s^2$
The mentioned acceleration of about $0.25m/s^2$ dwarfs that, and if at ...
- 2,863
26
votes
Accepted
What is the minimum size for the Sun?
Black body radiation
The Sun is, approximately, a black body. That means that the light it emits follows a particular spectrum according to Planck's law, with the shape of the spectrum determined ...
- 99.8k
24
votes
Accepted
Moons that can't see each other
In theory if the two moons were in the exact same orbit on opposite sides of the planet then yes. Having the moons closer to the planet and smaller also makes that easier. For example geostationary ...
- 77k
23
votes
Killing a star safely
A star shines because it has mass...
You put enough mass together, it gets a dense core, heats up, and voila, solar fusion. Yes, that's an oversimplification, but, fundamentally, making a star not ...
- 25.4k
23
votes
Is stealing the moon actually possible?
You can't move the Moon, it just requires too much energy. But maybe we can deny everyone else the Moon... and ALL OF SPACE!!!
Energy Required To Move the Moon out of the Earth's Orbit
Let's say "...
- 30.1k
22
votes
Accepted
Do seasons occur on a tidally-locked planet?
Yes, if the orbit isn't circular.
Seasons can definitely occur on a tidally locked planet.
Just like normal planets, tidally-locked planets don't need to have perfectly circular orbits. This means ...
- 99.8k
21
votes
Practicality of building a space station in the tail of a comet
The thing about the tail is, it's not in the same orbit as the comet. So you would need to use rockets (or whatever you use to move in space under the rules in your story) to stay in the tail.
A comet'...
- 4,137
20
votes
A planet illuminated by a black hole?
From Hawking radiation? No.
The Hawking radiation emitted is inversely proportional to the black hole's size. To make the black hole glow with enough light to be as bright as a star from Hawking ...
- 5,773
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