# Questions tagged [planets]

Celestial body that orbits following an elliptical path around a star or stellar remnant.

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### Numerical Solution of the circular restricted three body problem [closed]

I am trying to numerically solve the differential equations in the planar circular restricted three-body problem. In the rotating frame, the differential equations are given by \...
1 vote
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### Why does a moon's orbit get more circular with time?

I understand that there is a transfer of energy between a moon and a planet depending on whether the moon is orbiting faster or slower than the spin rate of the planet. This would obviously change the ...
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### What is the relationship between gravitation, centripetal and centrifugal force on the Earth?

I'm trying to analyze a situation wherein a ship is moving across the surface of the earth. I am trying to analyze this situation in a reference frame that is rotating with the earth (NED frame). I am ...
1 vote
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### The topology of planets [duplicate]

Just a curiosity: Let $g \in \mathbb{Z}_{>0}$. Is it possible for a planet of topological genus $g$ to exist? For example, is there any contradiction (from the point of view of physics) in assuming ...
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### Why are planets denser as you approach the center?

Gauss' law says that the net electric force inside a hollow, uniform, not rotating sphere is zero. Since gravity is also proportional to the inverse square of the distance, I assume this should apply ...
1 vote
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### Gravitational attraction between two bodies

While the gravitational force between two bodies is directly proportional to their masses, and inversely proportional to the distance between them is understandable / seems logical, how did Newton ...
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### Can we treat the entire mass of the spheroid as being concentrated at its center?

I know that to find the gravitational force between two objects, if either of them is a sphere, we can assume its mass to be concentrated at its center and use the formula for gravitational forces for ...
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### Despite tides the Moon, as far as I know, doesn't slow down. Where does the energy come from? [duplicate]

Hy, I don't have anything to do with physics, so please forgive me if I explain my question in a weird way ;) As the Moon rotates around the earth it is creating tides and waves on the earth. IE it's ...
8k views

### If gravity is not a force, what makes massive objects spheroid?

For most of my life, the explanation given for why celestial bodies like stars, planets, etc. are round is due to gravitational force. Simply put, if an object has enough mass, it will, in turn, have ...
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### Why are planets cold?

Excuse me for me ignorance, I'm just fiddling around this question for quite a while. The question of course is not limited to planets. Boiling down to, why isn't the universe heated up by now to ...
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### How symmetric do we know the gravitation field to be?

Currently, the only ways to measure gravity is on quite large scale. So these experiments measure gravity averaged between vast systems of particles. Of course, such an averaging results¹⁾ in a ...
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### Minimum size for a planet to have a molten core

What would be the minimum size for a planet or moon so that it would have a molten core? Gravity and density would play a part but how could this be worked out?
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### Magnetic compass working on the Moon and the Mars planet

Mars planet Moon Magnetic compass Theoretically and practically, will a magnetic compass work on the Moon and the Mars planet?
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### What regulates the size of our atmosphere?

Our atmosphere is only about 100km thick before the official start of space. That is a mere 1.57307% of the radius of Earth (6,357km). The difference between the gratitational force at sea level and ...
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### What are the odds of a rogue planet that enters into a galaxy reaching the black hole at the center of the galaxy?

I am wondering if anybody has ever calculated the odds of a rogue planet, which has been traveling through interstellar space and then enters into a galaxy, being able to travel all the way to the ...
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### Helium in Uranus atmosphere

I read that in 1986 Voyager 2 measured the composition of Uranus' atmosphere, which turned out to be composed of $85 \%$ hydrogen and $15 \%$ helium. It's not clear to me how this relevant amount of ...
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1 vote
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### How to calculate equilibrium height of tidal bulge?

I am trying to model the shape of the tidal bulge caused by the moon. I asked GPT for a formula and it gave me equilibrium tidal bulge height as $$\frac{2 R_{earth} G M_{moon}}{3 r^3 \Delta g}$$ and ...
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### What is the real shape of Earth? [duplicate]

As it now widely dicussed and accepted that Earth is not a 'perfectly round sphere/ball but more a 'oblate spheroid' why then do NASA have 'photographs' of a ROUND Earth?
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### Angular momentum of the Moon (or any body orbiting another orbiting body)

Let the Moon have angular velocity $\omega$ around the Earth. The Earth itself revolves with velocity $V$ around the Sun. The radius vectors are $r_i$ from Sun to a point on the Moon, $r_i'$ from ...
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### Exact analytical solution for the surface gravity of an oblate spheroid

I would like to know if an exact solution for the surface gravity force components of an oblate spheroid has been published and if not can anyone derive it here? Assume an ideal rigid oblate sphere of ...
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### Why is Earth a sphere? [duplicate]

Physicists and Physics enthusiasts . I am new to this platform. And I wanted to post a question . Since I have nothing in my mind. I wanted to ask , Why is the earth a sphere and not other shape? ...
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### What is the hydrostatic shape of an ideal rotating planet? [duplicate]

It is a well-known fact that rotating planets have a flattened spheroidal shape. However, the NASA site says about Haumea: The fast spin distorts Haumea's shape, making this dwarf planet look like a ...
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### Is either Geocentrism/Heliocentrism more "correct" than the other? [duplicate]

Yesterday there was a casual discussion of the findings of the scientist Galileo in my German class. It was mentioned that his breakthrough was that, he found a convincing explanation that earth ...
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### Why does a total solar eclipse happen every 18 Months?

What is the math involved in calculating how often a total solar eclipse happens. Can you predict it by just looking at the period of the moon around the earth and the period of the earth around the ...
1 vote
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### Holsapple simple scaling law [closed]

Could someone explain Holsapple's simple scaling law? Furthermore, is Holsapple simple scaling law able to be used on Earth in the context of dropping an object and measuring the impact crater size? ...
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### Estimate Saturn's mass [closed]

How can you estimate Saturn's mass using data from Cassini's final moments in September 2017 (apoapsis on September 12 at 1:27 a.m. EDT Saturn time at a distance of about $1.3*10^6$ km from Saturn, ...
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### Gravity formula inside a planetary core

I am trying to work through this problem so that I can understand how to convert from pressure values to radius values inside a planetary core in a code. The core has variable density depending on ...
1 vote
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### Atmosphere of a hypothetical planet

A hypothetical planet is 2/3 the radius of earth but has 1g surface gravity. Given the planet has the same surface gravity as earth, the atmospheric pressure would be the same. This would also mean ...
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### Why is sunset in mars blue?

This is the Martian sunset, as captured by the Spirit rover of NASA. Notice the colors are inverted, i.e. the direct rays blue and diffused rays red, which is exactly the opposite of what you would ...
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### Issue while understanding gravity/radius of earth graph [closed]

I have following question. What are my opinions? 1. Option 1 - This is incorrect. I think dotted line in option 1 from bottom to peak represents center to surface of earth. After the peak, line ...
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### How to measure the ratio of a planet's radius to a star?

I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information. One of ...
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