# Tag Info

### Post-war apocalyptic desertification scenario lasting at least 1000 years

Notes: Getting Earth to be a hot desert without killing all multicellular life is probably impossible. (It's the oceans. You have to get rid of them - and the only way to do that is to make Earth so ...
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Accepted

### Binary Star System Physics

Without a rigorous calculation, based on this equation, we can see that the gravity exerted on the Earth by the moon is about 2.2 times larger than the force exerted by the sun. I'm making the ...
• 351

### What would a beacon of light activated on Earth's surface look like from space?

You could see them.. if there were a lot of spaceships, spreading thruster molecules masses out there in the void. Basically, the equivalent of plane-trails in space- meaning, its very faint and ...
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### What would a beacon of light activated on Earth's surface look like from space?

Unfortunately, Nothing The reason we can see beams of light like spotlights on earth is because the light we are actually seeing is that being scattered by various particles in our atmosphere (...
• 351
1 vote

### 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 ...
• 89.1k
Accepted

### 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 ...
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, ...
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### 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. ...
• 123k

### I need to know day/night cyles of a moonplanet

You've got a bunch of unknowns here, some of which are more important than others. The size and mass of the primary star, which determines how hot it is, and how big it looks from your moon. The size ...
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### I need to know day/night cyles of a moonplanet

The moon orbits the planet, that's the most logical choice for the moon's year. The planet orbiting around the central star is not the primary choice, for someone living on the moon. More or less as ...
• 287k

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

At first thought, the absolute maximum apparent diamater of a companion world in the sky of a habitable world would have to be 180 degrees since if any portion of it appeared to extend more than 90 ...
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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 ...