Hot answers tagged

181 votes
Accepted

Would a Moon made of water pose a threat to Earth during eclipses?

The results are quite boring I'm afraid. The surface would freeze and turn a colour similar to many of the icy moons we see on our solar system. That is normally a sort of off-white or dirty grey. ...
  • 76.2k
181 votes

Would a Moon made of water pose a threat to Earth during eclipses?

Sorry, no spectacular death ray occurs for a number of reasons: The focal point is in the wrong spot Water absorbs nearly all the energy The angular diameter is insufficient 1. The focal point is in ...
  • 2,095
104 votes

Speedrun to the moon in one lifetime?

Impossible This is an extension of, or complement to, L.Dutch's answer, which was first. I upvoted it. So should you. I'm fond of reminding people that 99.99% of the technology we enjoy today was ...
  • 96.2k
103 votes

What could a self-sustaining lunar colony slowly lose that would ultimately prove fatal?

EDIT April 26, 2020 While searching through my answers for research related to another question I came across this answer. The irony that I wrote this one year ahead of the Coronavirus pandemic, which ...
  • 96.2k
87 votes
Accepted

How would having multiple moons affect tides?

TLDR You can model the effect of two moons by summing two sine waves. To do this plot each moon as a function of Time and manipulate the gravity of the moon by changing the amplitude and the orbital ...
  • 18.2k
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
82 votes

Can I use a trebuchet to launch satellites into space from a lunar colony?

No. No matter how much velocity you can give your satellite, its trajectory will either contain the point it was launched from or not be a closed curve. an object is in orbit if it returns to its ...
80 votes

Speedrun to the moon in one lifetime?

I don't think it's feasible. First of all, for anything they need, they might know what they need to build, but they have no way to reach the place where the raw materials are located. E.g. Jim: &...
  • 248k
65 votes

How would one design an undetectable nuke to hit the Moon with?

Why not? Make it a relatively dumb bomb on a timer, paint it black, give it radar absorbent plating, and (this is the important part) launch it from the far side of Earth. Your delivery system can ...
  • 24.8k
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 ...
  • 28.4k
60 votes
Accepted

Would gas giants work as waste disposal sites?

What you suggest is possible, but the solution is a major problem, for larger reasons. We have sent probes to crash into Jupiter. It is physically possible to send waste into a gas giant. Just as it ...
  • 20.1k
55 votes

Speedrun to the moon in one lifetime?

It can't be done. There's a famous phrase in project management, "Nine women cannot make a baby in one month." This is one of those cases where you just can't parallelize enough. The ...
  • 130k
54 votes

How big could an alien-made object on the far side of the moon become so that discovery still can only happen by accident?

Cover it in regolith The moon hasn't seen a lot of activity in the last few billion years, leading to it being mostly covered in a loose layer of fine dust, called regolith. This layer is 4-5 meters ...
  • 84.5k
54 votes
Accepted

How would you build a harbor in a world with *intense* tides?

LOCKS The answer is one that is used extensively today in canals and rivers: Locks. Locks are basically double water-tight gates. If you want to go from high water to low, you sail in, the gates are ...
53 votes

Can I use a trebuchet to launch satellites into space from a lunar colony?

It is possible...eventually To be clear @SilverCookie's answer is correct. In simple Kepler mechanics, when you give a single delta-v to an object there are two 'orbital' possibilities: the orbit ...
  • 84.5k
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. ...
  • 96.2k
51 votes
Accepted

Moons of Moons of Moons

Let's make a bunch of assumptions: The largest primary is about 3 times bigger than Jupiter. To really be a parent, the barycenter of a parent-satellite system must be within the parent. Everything ...
  • 843
51 votes

What could a self-sustaining lunar colony slowly lose that would ultimately prove fatal?

Materials exposed to vacuum for extended periods often become brittle and/or literally lose mass over time. Outgassing, cold-welding, decomposition of alloys back to their constituent materials, ...
  • 5,723
43 votes
Accepted

Moon that changes color with phase

Our moon is tidally locked so we only ever see one part of it (one rotation per orbit). But if your moon's rotation was instead matched to the phases then you would see the same part of the moon ...
  • 1,749
43 votes

What could a self-sustaining lunar colony slowly lose that would ultimately prove fatal?

A non-obvious loss area would be Genetic diversity. After several thousand years of carefully controlled plant growth, and several thousand years of inbreeding, unless care was taken to maintain ...
41 votes
Accepted

Can a radioactive moon affect life on a planet?

How to generate radiation Radiation by nuclear emission A moon made of some non-fissile (definitely not fissile!) transuranic element would emit significant alpha, beta, and/or gamma radiation. ...
  • 84.5k
40 votes
Accepted

How big could an alien-made object on the far side of the moon become so that discovery still can only happen by accident?

The latest publicly available moon map has a resolution of roughly 328 feet. Any object smaller than that would be a single pixel, and would be difficult to pick out from the background jumble. You ...
  • 14.9k
39 votes
Accepted

What's the smallest reasonable natural planet or moon with Earth-like surface gravity?

The densest reasonable material for a planet is iron The wikipedia page for the abundance of chemical elements breaks it down a dozen different ways, but any way you split it, by far the most common ...
  • 84.5k
38 votes
Accepted

Can you add a mini moon to Earth?

Note: If anyone can double-check my numbers and result at the end of this answer, that would be much appreciated. This looks like a question that can be broken down as per your bullet points, so I ...
  • 97.8k
37 votes
Accepted

Can we 'beam' energy from the moon?

I'll answer these out of order, since the first is much more difficult to address. Meltdown damage A nuclear meltdown of a reactor on our moon would probably not be very noteworthy. Human workers on ...
  • 2,212
37 votes

How big can a moon be where you can physically jump out of its orbit, to its planet?

No. You can't jump from a moon in stable orbit to the planet. This is because the orbital velocity of the satellite is sufficient to keep the satellite in orbit, the jumper starts with that same ...
37 votes

What skin colour would living permanently on the moon select for?

Random. I am reminded of the teeth of the numbat. http://animaldiversity.org/collections/contributors/anatomical_images/family_pages/dasyuromorphia/myrmecobiidae/ The numbat has more teeth than any ...
  • 287k
36 votes
Accepted

Tidally locked gas giant moon - brightness of the gas giant

I decide to simulate the situation in question. After trying Celestia and Kerbal Space Program with mixed results I stumbled upon Space Engine which turned to be an awesome tool for this. Below are ...
  • 753
36 votes
Accepted

Where is the best place to park your damaged spaceship, longterm?

The orbits of larger moons should be stable and mostly clear of hazards. I'd recommend placing your ship at one of their Trojan points. Just pick the one most convenient. Closer to planet, not already ...
36 votes

How would you build a harbor in a world with *intense* tides?

Some years ago I went to Scarborough (Yorkshire) and visited the local harbor during low tide: all the ships were sitting on wet sand, as shown in the painting below (for some reason I can only find ...
  • 248k

Only top scored, non community-wiki answers of a minimum length are eligible