Questions tagged [moons]

For questions pertaining to natural satellites, such as our own Moon.

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2 answers
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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

As I said in the title, I have a world with two moons. One has an orbital period of 17 days Earth days (Moon 1) while the other has an orbital period of 57 Earth days (Moon 2) and the planet they are ...
2 votes
2 answers
98 views

How to calculate the Draconic month on a fictional world

I am working on a world and want to be able to find out when Eclipses occur, and I found you need to know the Draconic Month, I think I have everything I need to find it, I have the inclination to the ...
0 votes
1 answer
57 views

How long would solar eclipses last on my moon?

On a moon of a gas giant, there would be a substantial amount of time where the giant blocks sunlight from reaching the moon. How do I determine how long this total eclipse would be? Notes: Orbiting ...
5 votes
3 answers
865 views

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

I wanted to give my planet a moon that spins every SIX days and waxes-wanes every THIRTY days. The bad news: Luna always shows the same face to Terra because of something called tidal locking ...
11 votes
10 answers
3k views

Permanent Full moon via "Magic"

The Problem I had in mind giving my world a permanent full moon for a long time. Though I generally ran into 2 problems along the way. Firstly I wanted of course to make it appear as if it was always ...
4 votes
4 answers
988 views

Moon calendar with a permanent full Moon

The Situation This can be considered a continuation of the following question: Permanent Full moon via "Magic" In this question I asked how a permanent full moon could be possible. While I ...
3 votes
1 answer
69 views

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

So I did the math and the crust would bulge 8000 meters due to being tidally locked. On Earth such an elevation would mean the air is extremely thin. I was wondering if the atmosphere would bulge ...
6 votes
1 answer
256 views

Non-deadly gas giant moon "weeks"?

There are already a lot of questions on WB:SE about habitable gas giant moons, so I'll try and be specific: I have a gas giant of mass approximately $2\cdot10^{27}\text{ kg}$ and radius approximately ...
5 votes
3 answers
229 views

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

I am trying to make a moon orbiting a large ice giant that has a liquid ocean via this thought process: The moon has high eccentricity (though it is still in spherical shape), so raw tidal forces ...
15 votes
3 answers
1k views

What is the largest possible appearance of a celestial body in the sky?

In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically, since there are maxima for the possible size ...
4 votes
1 answer
103 views

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

Based on the visibility of the Earth from the surface of the moon, I created this map. This shows where the gas giant would be visible from the surface of one of its moons. However, it's quite basic; ...
16 votes
3 answers
5k views

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

I know the Roche limit limits how close another planet could get to Earth. Closer than that limit, and either it breaks apart or Earth breaks apart. I don't care what size it is, if it's a super-...
2 votes
1 answer
215 views

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

On a tidally locked earthlike moon of a gas giant, would the side that faces towards the gas giant be noticeably warmer than the side that faces away? Would the gas giant generate enough heat to have ...
4 votes
3 answers
530 views

I need to know day/night cyles of a moonplanet

My moon planet is the moon to a gas giant in the habital zone of its red giant star, orbiting the same distance the earth orbits the sun. It is not tidally locked, being in opposite rotation of its ...
1 vote
2 answers
109 views

Would a moon that is tidally locked to a gas giant rotate at an axis?

Can a tidally locked moon have an axial tilt and have seasons like Earth? If not, what if the gas giant was tilted. Would the moon follow its tilt?
4 votes
1 answer
415 views

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

This is my first post. I apologise for any infractions I may have committed, I will try to be better in my next posts. To clarify, this question is not about if Earth had 'two moons'. This is instead ...
0 votes
1 answer
164 views

Various eclipses in a P-type binary star system?

Trying to make a world with a P-type binary star system, with a habitable planet orbiting around them, and one moon orbiting said planet. I am terrible with physics so I've been wondering if any of ...
2 votes
2 answers
133 views

Can you have a moon that rotates 21 times per orbit?

I want to avoid having my earthlike moon of a gas giant be tidally locked. Now I know that 3:2 or even 5:2 resonance is possible, but what about 21:1 for my moon? Is that too many rotations per orbit ...
8 votes
2 answers
3k views

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

I have an Earthlike moon orbiting a Saturnlike ringed planet at 1.8 million km. Neither the moon nor the giant are tidally locked. How bright would Saturn appear to be in the sky? Would it hurt your ...
11 votes
2 answers
5k views

Could a planet have 1/2 the Earth’s mass but 1 g surface gravity?

So, we have a captured planet/moon orbiting a gas giant in the habitable zone. It is akin to prehistoric Mars, its geological activity having been maintained by constant tidal flexing from the gas ...
7 votes
1 answer
273 views

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

Imagine an earth-type world orbiting a Jupiter-like gas giant roughly within the habitable zone. If the plane on which the moon orbits the planet is tilted at an angle relative to the Solar System's ...
5 votes
3 answers
147 views

How small can you make a planet or moon and still have dust devils on its surface?

I want a moon for one of my planets to be larger than the Moon, enough to have an appreciable atmosphere, but not quite so massive as Mars. I'd like it to be that if you were to land on it, the thin ...
7 votes
5 answers
2k views

How much mining can we get out of Pasiphae?

Pasiphae is an irregular moon of Jupiter in a retrograde orbit. It's probably an asteroid capture and is only about 60 kilometers across (compare to Europa's 3121.6 km diameter). Suppose that I set up ...
21 votes
1 answer
3k views

Plausibility of a gas giant moon

Is it plausible for a mini-Neptune to form around another gas giant? How big would the main gas giant be to accomodate such a moon?
7 votes
2 answers
333 views

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

This is an earth-sized planet, unable to produce an adequately protective magnetic field. Could a moon with a hot, iron/nickel core produce a magnetosphere large enough to encompass the planet and ...
1 vote
3 answers
226 views

Is it possible for a moon to have a river flowing across one giant continent?

I’m creating a world where one giant supercontinent has a river flowing across it. The land is covered in lush forests and is surrounded by mountains. The world is orbiting a gaseous planet and is ...
3 votes
2 answers
118 views

How do I figure out where a moon is in the sky at a given time and place?

I use this planetarium tool to see the position of the Moon to check I have it in the right place for a given place and time, for my non-Earth plant. I'm considering having another moon. How would I ...
2 votes
1 answer
140 views

Could one moon appear to always follow/lead another in the sky?

Is there any way a second moon would appear to hang out near the closer one in the sky? For example always appearing either ahead of or behind throughout the year, or even alternating between those ...
2 votes
3 answers
262 views

Question about speculative human biology

What kind of evolutions would humanity have to undergo to be able to live comfortably on the moon or any other sufficently low-mass body? As I am aware that it can be bad for bones and the ...
5 votes
2 answers
274 views

On Habitable Moon Systems

Context I was working on a habitable gas giant moon, but I came across an issue in that, at the acceptable distances from its parent planet (10-20 planetary Radii, according to an Artefexian video on ...
0 votes
0 answers
33 views

Size of parent planet in the sky from a tidally locked moon [duplicate]

TLDR: Can anyone explain to me (like I am five and very bad at math, the latter of which I actually am) how to determine the size of the parent gas giant in the sky of my moon? EDIT: I am asking for ...
5 votes
0 answers
88 views

What is the largest apparent size a moon of a habitable planet can have? [duplicate]

Inspired by this question: How large can an apparent size of a moon be? I am looking for a moon that is: a terrestrial moon with properties vaguely similar to Luna (not a binary planet, but it can be ...
1 vote
0 answers
91 views

How do I make a Lunar Calendar for a planet with three moons and two suns on either side? [closed]

The planet is about three to five times the size of Earth and it shares a solar system with 13 other planets and they have an ∞ shaped orbit around two suns on opposite sides of the solar system. The ...
-1 votes
3 answers
134 views

How would a government lay claim over a Space Colony that it never founded? What legal arguments could they make to cite it’s always been theirs? [closed]

I’ve read some books with a premise of leaving an increasingly centralized and decadent Earth for the stars before it heads a turn for the extra worse Part of their premise is Earth Governments ...
9 votes
3 answers
314 views

Is it possible for a planetary ring to exist beyond a planet's Roche limit?

So my story takes place on a moon orbiting a gas giant about the size of Jupiter and I was wondering if it was at all possible for a planetary ring to exist beyond the planet's Roche limit. I ...
5 votes
2 answers
462 views

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?

Is it possible to have a stable system wherein the moon of an Earth-like planet is visible only during certain parts of the year (seasons) from a fixed point on the surface, mimicking the way some ...
2 votes
2 answers
228 views

What astronomical situation could account for the PERCEPTION of a very erratic day / night cycle for a planetbound population with limited science?

I would like to create a world that is at a roughly medieval level of scientific understanding and which - as far as it appears to the inhabitants of that world - has a highly erratic day and night ...
3 votes
2 answers
244 views

Could Moon Phases work in a Concave Hollow-Earth?

I'm trying to wrap my head around how phases of the moon(s) would operate in a hollow earth. For reference, I am picturing a situation like this: In this system, the center of the hollow earth has a ...
2 votes
3 answers
384 views

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

Europa, one of Jupiter's moons, is 4.5 billion years old (like Earth.) However, its surface is only 20-180 million years old. What could lead to a planet/moon's surface being younger than the planet/...
5 votes
1 answer
171 views

Habitable Planet with Multiple Moons

I am working on a book with the presence of multiple moons acting as a quasi-astrology based religion whereby the irregular phases of the moons and their relationships between one another allow for '...
1 vote
0 answers
90 views

How can an Earth-like planet support two moons of different sizes [closed]

In my world, I need to have two moons orbiting an Earth-like planet. I need the extreme tides as they play a big part for a cultural detail. The first moon should be roughly the size of our own moon, ...
7 votes
1 answer
178 views

Would tidal recession significantly reduce the angular size of small moons?

Multiple large moons around a terrestrial planet is something that is seen in science fiction a lot, but is not really easily possible. An alternative is to use smaller moons but have them orbit ...
120 votes
7 answers
43k views

How would having multiple moons affect tides?

We know that planets can have multiple moons, sometimes quite a few (like Jupiter). Assuming that a planet with several moons were habitable in the first place and has significant oceans (greater ...
2 votes
2 answers
126 views

How to find visibility of stars given a certain moon brightness

How would you be able to calculate what magnitude of stars would be visible given a certain brightness of the moon. As I know that the visibility of stars are based on their compared magnitude to a ...
0 votes
2 answers
102 views

Question about finding an exact lunar orbit

I am trying to find a precise orbit for a moon that would allow it to always be in an eclipse. So, basically, I need help finding a formula for the semi-major axis and mass ratio that would get the ...
2 votes
2 answers
159 views

Red Dwarf Gas Giant Moons?

I'm thinking of an idea for a Red Dwarf star to have one (perhaps even two, but that would obviously be very unstable) Jovian Gas Giants with Mars- to Earth-sized moons in the habitable zone. The idea ...
0 votes
0 answers
91 views

Can there be habitable moons despite heavy changes in axial tilt of their mother body?

Ok so i created a gas giant with 10 Jupiter masses and like 9 moons between 0.8 and 1.5 earth masses. All exept the most distanced of those moons are tidally locked to the gas giant and their axial ...
3 votes
1 answer
127 views

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

I believe it is true (correct me if I'm wrong) that a planet with a significant moon such as ours cannot be tidally locked. The orbit of the moon would continue the rotation of the planet and must, ...
2 votes
1 answer
88 views

Exomoon Color as Viewed from Planet It Orbits

I have been designing a planet and it has one moon that is slightly smaller than ours. Just like how mars appears red and its dust is red, I realized that maybe if I altered the composition of my moon,...
4 votes
2 answers
143 views

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?

Imagine a earth-like planet where life is beginning to thrive at the bottom of the ocean. So far it is an elegant carbon-based lifeform, not different than the one that has burst in our earth. But ...

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