# Questions tagged [astrophysics]

For questions regarding the application of the laws of physics to orbital mechanics, stellar evolution, and other astronomical processes and celestial bodies.

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### Could an earth-like exomoon orbit around a bigger earth-like planet? [closed]

Quite basic I know but what can I say? Need to be sure.
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### How can we prevent the Earth being scorched and swallowed as the Sun grows and eventually enters its red giant phase?

The Sun is slowly growing more and more luminous. As a result of these processes, multicellular life forms may be extinct in about 800 million years, and eukaryotes in 1.3 billion years, leaving only ...
1k views

### Would two people standing on opposite sides of a flat world be able to see the same constellations?

Quick drawing illustrating what I mean: Two people (humanoids, between 1 and 2 metres tall) are standing on the ends (less than 1km from the edge) of opposite faces of a flat world (approximately ...
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### Tides on a tidally locked planet

Picture the classic Earth-like tidally locked planet, with a frozen dark side, a boiling stormy light side, and a thin strip of habitable land along the terminator. The planet is similar in size and ...
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### How would a planet with three suns, orbiting only one work?

Okay, I am planning to make a planet that has three suns, and orbits one of them. Each of the suns has its own orbital path, so it's possible for the planet to have one sun, two suns, or three suns in ...
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### Where could we add a new planet to the inner solar system?

Assume there was a super advanced alien race that for some reason, wanted to add a new planet, of lets say 1 Earth mass, into the Solar System. Where in the inner Solar System (The part of the solar ...
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### What is mathematical formula for finding the mean surface temperature on a planet in our solar system?

This question is to assume the common solar luminosity of approx $4 \times 10^{26}$ Watts. The mean flux of Earth at, for example, 1.1 AU would be about 1176 watts--but how can I calculate mean ...
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### What is a reasonable day length for a planet with 4 times earth radius?

The fictional planet has a mass of 18 times Earth's and four times earth's equatorial radiusreference. This gives it a gravitational acceleration of 11.02m/s^2 (1.29G) and an escape velocity of 23....
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### Obliterating the Earth, *without* throwing rocks? [closed]

In this case, I don't mean "make the Earth uninhabitable", I mean "make the Earth a debris field". This has been asked before, of course, but the answers always seem be be some ...
116 views

### How large can the main disk of spiral galaxies get? [closed]

I'm asking how large (by which specifically I mean diameter in light-years, though a rough estimate of the number of stars would be appreciated) can the main body of the spiral galaxy get. I'm ...
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### Dealing with extreme heat and pressure in an underground colony on Venus

A colony has been constructed by robots for human habitation deep under the surface of Venus. They are totally sealed off from the surface, and the galaxy beyond, and live like a ship in a bottle What ...
102 views

### How long would Earth be habitable after being knocked out of orbit? [duplicate]

Let’s say a rogue planet or something came close enough to Earth to knock it out of its orbit. Whatever event causes this, can this happen without disrupting human life in the short term and how long ...
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### How would a spaceship not affected by gravity navigate between planets?

Presume there exists a metal called X-matter that has all the properties of steel, except it is repulsed by normal-matter instead of attracted. (For instance, a block of it would accelerate 9.81 m/s/s ...
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### Galactic 'geographic' features, how could they impact galactic colonization efforts?

I have been wondering how galactic features could impact interstellar civilizations in the process of colonizing a galaxy (either andromeda or the milky way). According to this video these features, ...
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### What are the effects of Increasing the gravity on Mars?

I'm interested in the Physics around increasing the gravity of Mars to make it habitable. I was unsure how to work out what gravity would be needed to retain an atmosphere thick enough to hold liquid ...
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### How to place multiple small moons and one large moon in stable orbit around an earthlike planet?

Earth has one very large, spherical moon believed to have been formed by a giant impact. Mars has two small, sorta potato-ical moons believed to have been captured. Suppose an otherwise earthlike ...
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### Can moon people generate electricity using a gravity dynamo that is turned by the gravity of their host planet?

On Earth, we generate electricity from the Moon's orbit using tidal turbines. Would it be possible for denizens of the Moon to generate electricity using the Earth's gravity, using a windmill-sized ...
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### If Earth had a smaller radius, but was rotating at the same speed, would its day be shorter?

I want to make a hypothetical planet that is 26% the mass of earth, with 64% the radius. Because I want a relatively short day to keep temperatures more stable, but I don't want a super fast rotation ...
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### How would a high escape velocity effect conditions on a low gravity Birch planet?

A birch planet is a theoretical far future Giga-structure where a shell world is built around a supermassive blackhole. I have been playing around with different astrophysical calculators to find out ...
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### What kind of atmospheric composition would make the sky look green and still be breathable?

In my story scientists discovered a planet that look green from the telescope and they used a advanced starship to go there and the y found out that the planet is habitable with a breathable ...
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### What would happen if a neutron star approached the solar system?

Given its enormous eletromagnetic field and gravity( and probably gravitational waves would be very powerful) what would happen if a neutron star approached Earth? What if approached just by few light ...
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### Day/night cycle and tracking celestial positions in S-type binary star system

I know this has been asked before but I'm going to pose the question again under slightly different circumstances and with a more specific goal. I'm trying to work out the details of how the day/night ...
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### Could a molecular cloud turn the Sun into a killer star?

Let's say an unknown cloud enters the Solar System and begins manipulating the Sun, destabilizing the magnetic fields. Could it end up causing the Sun to emit gamma ray bursts to render the system ...
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### Figuring out the precise location of Earth a certain amount of time ago

Movement is relative, but I've read that an ex-NASA scientist has quantified the speed of Earth hurtling through space to be 1.3 million mph, using the Cosmic Microwave Background as a frame of ...
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### how plausible is this exomoon?

(this is doublet of my previous question, so I did a little improvement on it) -my exomoon is around size of venus, but a little bit smaller. is very windy, so windy in fact filter feeders thrives in ...
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### What are the odds of a binary solar eclipse?

I'm currently creating my own binary star system which includes a circumbinary planet that has two moons. For simplicity's sake, the stars, planet, and moons are comparable in size to our own Sun, ...
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### How could a galaxy be damaged by a civilization's industrial expansionism in ways that mirror our own current climate crisis?

There are several stellar environmental results from sentient industrial over-expansionism that I can imagine ie. star lifting that results in entire systems becoming frozen husks and debris from ...
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### Could there be biomes inside of asteroids?

I don't mean "biome" in the strict scientific definition, but rather, in the broader geological sense that it is used by game designers to refer to unique environments. On earth, when people ...
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### Could the electrical charge of a black hole neutralize it's gravitational pull?

It's well-known that gravity is the weakest of the 4 fundamental forces. With this knowledge, would it be possible to cancel out the gravitational forces of a black hole with it's charge? Say a black ...
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1 vote
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### Relative masses of Binary Systems

I'm writing a sci-fi novel and I have an some astrophysics questions. First, is it possible for a binary system to be made up of a large gaseous planet and a dwarf star? I know it's possible to have ...
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### Where should I place my Earth-like planet within my binary system?

I am working on a RPG setting which requires my planet having a nearby flare star. I understand from reading through other, similar questions and from doing some research, that flare stars are ...
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### Days with a torus shaped Sun

What would day and night look like on Earth (or any habitable planet), if the sun was torus shaped, with the same circumference? And moreover, how much the Earth will be affected, if the sun was ...
1 vote
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### Two celestial bodies tidal locked - not with the sun

I tried to do my homework and actually thanks to this question and answer, I found myself to this site. But I just found more questions :) Basically the setting would be close to what Earth - Moon is, ...
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### Is delta v relevant for interstellar travel for generation ship?

Imagine I have a generation ship that is heading to a nearby star system say 10 light years away, the average lifespan for the crew is 150 years on Earth and is expected to increase by about 5 years ...
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### How Far In Advance Could People See A 100-1500 Meter Earth Bound Impactor Before It Hit

How much advanced notice would we likely have in advance of an Earth bound impactor with a place of origin outside Earth's orbit (e.g. a meteor, asteroid, comet, space debris that doesn't rotate ...
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### What Size and Likelihood Of An ET Impact Would Destroy A Small County Sized Region But Not Our Species?

Motivation The question is inspired by the astronomy journal preprint released publicly today, entitled: From impact refugees to deterritorialized states: foresighting extreme legal-policy cases in ...
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### Time scale and mechanism to “realistically” remove Sol from the Milky Way

What is the fastest rate a star could be flung out of our galaxy and by what mechanism(s)? (i.e. from a gravity kick by a hypothetical passing hypervelocity black hole) Secondary question: how far ...
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### How could a human with infinite strength crash a planet into earth

A bad guy was kicked off earth and lands on another planet or dwarf planet. He has magical powers that let him have as much physical power as he needs to accomplish his goals. He is also extremely ...
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### How big can a whirligig/planetcake get while still maintaining human-survivable gravity at its equator?

A whirligig/planetcake/whatever punny name you want for it is a super-sized planet (we're talking about Jupiter masses here, not Earth masses) that spins so quickly that it's shaped like a pancake (...
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### What would the local effects/affects be of a ring spinning near luminal velocity?

To better solicit more inline with what I'm trying to imagine, I'm editing my question, the original question is left below and removing the hard science tag, as that just seemed to cause issues, ...
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### Moon hit strong enough to put it in a slow spin?

I’m building a world nearly equal to earth; i need a catastrophic event that make the moon start spinning breaking the tidal lock, a really slow spin, like 500 years for a full spin. i thought about a ...
262 views

### Aliens pressure cook the Solar System, do we notice?

550 million years ago, aliens erected a spherical barrier 1/6th of a light-year (~10,000 AU) in radius around the solar system, centered on the solar barycenter. Things outside the barrier can enter, ...
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### Enlightening Dark Matter?

As an ironic twist, I wanted a story in which dark matter is actually caused by light. Somehow, the physics of light cause it to create the appearance of the existence of dark matter. But I'm not a ...
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1 vote
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### Would a gigantic meteor impact in the Strait of Gibraltar create a peak-ring crater, or at least a complex one?

Background: A peak-ring crater is a sub-type of complex crater (an impact crater in which the impact wave rebounded from the rim of the crater and pushed up a mountain in the middle) where, instead ...
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### Would a meteor blowing up the Strait of Gibraltar 2 million years ago kill all of humanity's ancestor species?

Let's say that, 2 million years prior to the present day, a meteor impacts roughly in the middle of the Strait of Gibraltar. It is large enough and strikes at sufficient velocity to create an impact ...
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### Effects of magic on stellar evolution

I believe it'd be foolish to assume that magic wouldn't affect astronomical phenomena like stellar evolution, But since I'm not smart enough to create the equations for a new fundamental force, I have ...
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### What would happen if a planet gradually lost mass?

The idea I have is to have a planet that, at its core, has a being that gradually eats away at the planet's substance and converts it into massive amounts of energy (think matter-antimatter ...
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### Estimating thrust and kg fuel for a generation ship's journey to Alpha Centauri

Premise: A generation spaceship leaves Earth around the year 2060 on a journey to colonize Alpha Centauri A (ACA). In this fiction, fusion power is achieved in 2040, improved over 20 years, and used ...
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### What would be the structural impact of an oscillating orbit on a planet?

Notice : If you wish to know how to make an oscillating orbit with real-world physics, you can looky-look at this question which is following mine. My question focuses on the consequences of such ...
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