Skip to main content
31 votes

Permanent Full moon via "Magic"

The moon orbits the L2 Lagrange point. L2 orbits conserve energy and momentum, but they are not stable equilibria; over large periods of time they will always evolve into eccentric elliptical orbits. ...
g s's user avatar
  • 7,277
29 votes

Plausibility of a gas giant moon

This is an interesting question. I'd argue that the answer is only a maybe through standard moon formation channels, but a clear yes if you accept more exotic pathways. The giant planets in the Solar ...
HDE 226868's user avatar
  • 101k
28 votes
Accepted

What is the largest fraction of Earth's sky that an astronomical object could take up (visually) before ripping Earth or itself apart?

The calculation turns out to be pretty straightforward and relies on two equations. Say the two objects have masses $M_p$ and $M_s$, with radii $R_p$ and $R_s$, with the $p$ denoting the more massive ...
HDE 226868's user avatar
  • 101k
21 votes
Accepted

Permanent Full moon via "Magic"

If you want it to be visible every night and don't mind it not being visible during the day, then it's easy: the Moon stops orbiting the Earth at its normal speed and instead takes up a position ...
N. Virgo's user avatar
  • 6,025
16 votes
Accepted

How much mining can we get out of Pasiphae?

I'd say only a few percent of its mass could be mined, but only because of the amount of material actually worth mining -- there's not really a risk of a potential collapse. The key point is that I'm ...
HDE 226868's user avatar
  • 101k
14 votes
Accepted

Everyone knows not to look at the sun. What about a gas giant?

We have a sun-like star and a planet at earth-like distance from the star, with paper-like albedo. Therefore looking at the planet when there aren't any clouds is like looking at an equivalent solid ...
g s's user avatar
  • 7,277
12 votes

Power grid on the Moon

While taking an economics course in college, we were divided into groups and asked to write a decision paper explaining our choice for how to dry one's hands in a bathroom to executive management. ...
JBH's user avatar
  • 124k
11 votes

How would a planet's surface be younger than the planet itself?

In short, you need a process that keeps renewing the surface. One of the reason is plate tectonics. For this very reason also Earth surface is younger than the planet itself, and finding very old ...
L.Dutch's user avatar
  • 289k
10 votes

How much mining can we get out of Pasiphae?

Mining station vs. mining colony Minor frame challenge: why a mining colony on the surface? To my knowledge, the approximately $\frac{1}{445}$ of a G of gravity on Pasiphaƫ's surface does essentially ...
KEY_ABRADE's user avatar
  • 12.8k
10 votes

Everyone knows not to look at the sun. What about a gas giant?

Quick answer: if you are okay with being out on your planet during the day, it should be fine to look at a gas giant. The gas giant will look as bright as a matt light grey card with an albedo of 0.42 ...
Richard Kirk's user avatar
  • 9,489
10 votes
Accepted

Moon calendar with a permanent full Moon

Here's one suggestion: have the moon spin. If the moon is rotating about any axis, then while it's held stationary landmark craters or divots on the Moon will visibly move around. If you line the Moon ...
controlgroup's user avatar
  • 4,786
9 votes

How much mining can we get out of Pasiphae?

You can mine it all. once they mine Pasiphae to the point that it starts to collapse in on itself, they have to evacuate to orbit 60 kilometers across is just a big lump of loosely connected ...
L.Dutch's user avatar
  • 289k
9 votes

What are the tidal implications of The Moon having a moon?

On Earth: no detectable effects. Deimos's mass is about 50 million times less than the Moon's, so its influence on Earth's tides is also about 50 million times less, regardless of whether it is a bit ...
g s's user avatar
  • 7,277
9 votes

How is this possible: a moon with A) large apparent size B) that spins C) spins in a 5:1 spin-orbit resonance?

TL;DR While a 5:1 resonance between the rotation of the Moon and its orbital period is possible (albeit quite unlikely), it won't help. Long explanation A lunar month, or a lunation, is the time ...
AlexP's user avatar
  • 90.6k
8 votes

I need to know day/night cyles of a moonplanet

We can't give you hard numbers without orbital and rotation speeds, but we can give you advice about figuring out the solution. This is more valuable to the worldbuilding community at large, anyway. ...
JBH's user avatar
  • 124k
8 votes
Accepted

Non-deadly gas giant moon "weeks"?

Radiative cooling times for moon-sized things are long. The formula looks something like this: $$t_{cooling} = \frac{Nk_B}{8\sigma\epsilon\pi r^2}\left[ \frac{1}{T_{final}^3} - \frac{1}{T_{initial}^3} ...
Starfish Prime's user avatar
7 votes

How could an Earthlike planet have two moons, one similar to the Earth's moon and the other primarily composed of carbon?

Depends on multiple factors Carbon doesn't exist in its pure state. It exists as carbon dioxide, methane or other compounds. Carbonates, while still present in space, are ultra-depleted, meaning that ...
Alastor's user avatar
  • 3,422
7 votes
Accepted

Could a cold-cored planet be protected by a hot-cored moon?

The moon magnetic field would protect the moon from the flow of charged particles coming from the star. Only in certain configuration of the moon - planet - star the moon could incidentally shield a ...
L.Dutch's user avatar
  • 289k
7 votes
Accepted

Is this a plausible way for an Earth-like exomoon to have earth-like seasons?

The answer is a yes! We know moons that have orbits like that and should experience seasons, and we know what needs to happen for them to form. Take a look at the moons of Jupiter -- and in particular,...
HDE 226868's user avatar
  • 101k
7 votes

Permanent Full moon via "Magic"

A Few Issues The largest is this: Secondly i wanted this full moon to be visible on the entire planet at least every night. It can't be "at least every night". It has to be at most every ...
jdunlop's user avatar
  • 32k
7 votes

Permanent Full moon via "Magic"

In Need of a Moon are You? Allow us of Bespoke Worlds to introduce you to our astounding line of Subplanetary Objects! Moons of every shape and description from large planet sized objects right down ...
elemtilas's user avatar
  • 40.6k
7 votes

Moon calendar with a permanent full Moon

Annual Moon Reckoning Terrestrial year calendars often make use of the Sun to determine when a year ends and a new one begins. Such as watching for sunrise on the solstice kind of thing. This, of ...
elemtilas's user avatar
  • 40.6k
6 votes
Accepted

Is it possible to have an ocean moon orbit a large ice giant via tidal forces and a greenhouse effect within the moon?

This is definitely possible -- largely because we believe similar mechanisms affect planets! Simulations have shown that some planets may become "tidal Venuses" (Barnes et al. 2013) thanks ...
HDE 226868's user avatar
  • 101k
5 votes

Living in natural satellite having an orbital period of 90 earth-minutes to a gas giant that covers all light. How would animal hunters thrive?

Short Answer: Life on your planet is doomed. The closest I could come to your requested 30 minute orbital period without dooming all life on the planet, and while having a reasonable chance of the ...
M. A. Golding's user avatar
5 votes

Power grid on the Moon

Just store the power. No, you do not want to use a bunch of expensive batteries when storing 15 days worth of power at industrial scales. What you want to do is store your power at an very large ...
Nosajimiki's user avatar
  • 95.1k
5 votes
Accepted

Could Moon Phases work in a Concave Hollow-Earth?

If you look at a model of our Solar System, you will notice that we observe phases only for the bodies (Mercury, Venus and Moon) orbiting between the Sun and Earth, due to the relative positions they ...
L.Dutch's user avatar
  • 289k
5 votes

Is it possible to have stable system where the moon of earth-like planet is only visible part of the year from a fixed point on a surface?

I think that is what happens when the planet is close to the point of becoming tidally locked to its moon: when the duration of a revolution around its axis is close but not the same as the duration ...
L.Dutch's user avatar
  • 289k
5 votes
Accepted

Would a gas giant have a warming effect on the climate of its moons?

You can apply the Stefan-Boltzmann law to estimate the luminosity ($L$) due to thermal radiation. The law is $L = \sigma A T^4$, where $\sigma = 5.67 \times 10^{-8} \, \text{W}\,\text{m}^{-2}\,\text{K}...
cconsta1's user avatar
  • 1,279
5 votes
Accepted

On a tidally locked moon of a gas giant, how do I determine the giant's position in the sky in a given location?

Lets assume that both your moon and the gas giant it orbits are spherical. That's likely to a real-life moon, but gas giants tend to exhibit noticable flattening (Saturn's polar radius is about 10% ...
Starfish Prime's user avatar
4 votes

Can a tidally locked planet with two counter-orbit moons exist for at least 100,000 years?

So, obviously this depends a lot on the initial conditions. For simplicity, lets assume the ideal case of two moons, one half as massive as the other, on circular orbits around a central body. Like ...
ErikHall's user avatar
  • 2,466

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