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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
  • 3,696
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
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8 votes
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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
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
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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
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6 votes
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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
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5 votes
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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

On a tidally locked moon of a gas giant, would the atmosphere bulge along with the crust?

The shape of a celestial body is dictated by an equilibrium of forces. I.e. planets are spherical because they are in hidrostatic equilibrium, but due to rotation they are larger at their equator, ...
L.Dutch's user avatar
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4 votes

How to calculate the Draconic month on a fictional world

Here's the equation for the Draconic month length Tn where: e is the eccentricity (note that the equation only works when this is close, but not equal to zero) a is the semi-major axis u is the ...
Mathaddict's user avatar
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4 votes

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

Your question is basically whether a 5:1 spin-orbit resonance is possible, and the answer seems to be 'yes', even if we don't have any confirmed existence proof in our own naturally created solar ...
geometrian's user avatar
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3 votes
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I have a world with two moons, and I was wondering how often they would both be full at the same time

If you have multiple moons and want to keep track of them, I'd suggest using a fantasy calendar. With one, you can get the exact places of the moon, as well as other helpful features. There is a ...
ShadowOfHassen's user avatar
3 votes
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Surface Hot-springs on an Icy moon

Yes, this seems quite plausible, based on what we know from observations of Saturn's moon Enceladus. Enceladus is quite icy, like Europa. Unlike Europa, it is known for its magnificent assortment of ...
HDE 226868's user avatar
  • 101k
2 votes

Surface Hot-springs on an Icy moon

I started this as a comment, but it is too long. It is theoretically possible for life to exist within an icy moon of a giant planet, if conditons are right, in hypothetical liquid water oceans ...
M. A. Golding's user avatar
2 votes

I have a world with two moons, and I was wondering how often they would both be full at the same time

The duration of a sidereal year of the planet is given as "about" 1.4 Earth years, or about 1.4 × 365.256 ≈ 511.358 days. Then the duration of a full cycle of phases for Satellite One is 17 ...
AlexP's user avatar
  • 89.7k
2 votes

Moon calendar with a permanent full Moon

Somewhere there's a world named Firth that has two moons, called Makoon and Maloon, with a beautiful calendar that was originally inspired by the interplay of the phases of these two moons. On that ...
David K's user avatar
  • 573
1 vote

How to calculate the Draconic month on a fictional world

The draconic month is equal to a sidereal month (= orbital period of the satellite) minus the precession of the nodes during that sidereal month. If you know the period of the nodal precession of the ...
AlexP's user avatar
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1 vote
Accepted

How long would solar eclipses last on my moon?

Quick and dirty Let's assume that the gas giant is sufficiently far away from the star that the diameter of the shadow at the distance of the satellite is approximately equal to the diameter of the ...
AlexP's user avatar
  • 89.7k
1 vote

Moon calendar with a permanent full Moon

Executive summary: Use the motion of the moon against the stars, with a healthy dose of divine intervention to make everything come out nice and neat. So you have, first of all, angels who keep the ...
David K's user avatar
  • 573
1 vote

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

Yes, that works. As comments will point out, moons similar to what you're looking for - Europa, Ganymede, Titan, Io, etc. - all have very interesting properties similar to what you described but are ...
controlgroup's user avatar
  • 3,696
1 vote

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

One half Since you're not asking for a solid or at least contiguous object, and you explicitly state any, the answer is M31 at its closest; it spans as much as you can imagine, also it has thickness, ...
Vesper's user avatar
  • 7,517
1 vote

Permanent Full moon via "Magic"

That's no moon, that's a plot device What if the moon is not a moon at all but a celestial traveler hiding in the shadow of the planet because the magical energy source of the sun is toxic to it. ...
Amish Cyberbully's user avatar

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