# Tagged Questions

The path a body takes while moving through space under the influence of the gravitational forces of other bodies

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### Calculate the speed of Halley's comet at his perihelion [on hold]

Knowing that Halley's comet orbita the sun every 75,3 years, that the semi-major axes is 17.83 AU, the semi-major axes is 4.53 AU and at his perihelion he is 0.586 AU away from the sun. With these ...
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### If we threw a baseball from the ISS, could we deorbit the ball?

Clearly this is a hypothetical question. Say we bring a star baseball player into NASA, prep them appropriately for a mission in space, and fly them up to the International Space Station. They go on ...
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### How would I find the velocity of an object after it doesn't fully enter the gravitational pull of a planet and is kind sling shot out of its gravity?

Obviously that question doesn't have a lot of jargon having to do with math and physics. I am not a physicist, I'm not a mathematician, I'm trying to make a game and simulate some physics found in ...
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### Is it possible for a particle to orbit a singularity inside the event horizon [duplicate]

Event horizon just means a distance from singularity, where there is no "going-away" from the black hole. But is it possible, that there are particles with enough momentum to actually orbit the ...
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### Tidal heating of body

I am trying to make a plausible, though not necessarily accurate model of tidal heating of a body moving close by a gravitational attractor, not necessarily in orbit and not considering the spin of ...
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### Experiment proving that the Earth is rotating around the Sun [duplicate]

Is there any simple experiment done on Earth proving that the Earth is rotating around the Sun? Something in the same spirit of what Foucault did proving that the Earth is rotating around itself. ...
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### Mathematically calculate if a Planet is in Retrograde

How do you mathematically calculate if a Planet is in Retrograde when you are given both the Earth and the Planet Keplerian Elements value and rate? Keplerian Elements are: a - Semi-Major Axis; e - ...
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### Determing Velocity of Moons

I have a question that I believe is relatively easy to answer, I am working on an $N$-body simulation of a fictional star system and am having trouble finding the velocity of moons so that they will ...
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### Simulation of relativistic probe passing through an external solar system

I recently read about the Breakthrough Initiative to launch "StarShot", a nano-probe that is designed to travel to Alpha Centauri at $0.2c$. One of the challenges to be solved involves the precise ...
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### Which force transfers angular momentum in tidal locking?

The moon is in tidal lock with the earth, but a long time ago it was not. As the moon became tidally locked with the earth, its angular momentum changed and the delta went into it's orbit and possibly ...
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### Relationship Gravitational Potential and the Tangential Velocity of a Satellite

So gravitational potential is given by $V(r)={\frac{GM}{r}}$ and the tangential velocity of a satellite is the square root of $V$, i.e. $\sqrt V$. So how do these two relate, if at all?
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### Derivation of Bohr model equations (1) in his original paper

My question is rather straightforward. In his original paper ("On the Constitution of Atoms and Molecules") Bohr provides equations (1) for the frequency and major axis orbit: \begin{align} \omega ...
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### Finding mass with an estimated gravitational force

As asteroids orbit the sun, they experience gravitational force exerted on them by the sun, and they in turn exert a very minute force back on the sun. Because of their small size, asteroids don't tug ...
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### Vector interpretation of Kepler's 2nd law ( r X a = 0 )

I just read the vector interpretation of Kepler's second law and the conclusion put me in a confusion. The interpretation concludes by demonstrating that r X a = 0, where boldfaced r and a are ...
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### Why are objects (such as planets) in motion and not static? [duplicate]

I am just curious, why are all the planets, rocks etc in motion? Would they fall into objects with larger gravity if they were not in motion? What is stopping the earth from falling into the sun or ...
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### Kepler's laws to determine radius of circular orbit

"In nonrelativistic limit of general relativity there is a correction to the Newtonian gravitational potential energy $−h/r^3$ with $h = αL^2/(mc)^2$, where $c$ is the speed of light, $α = GMm$ ...
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### How can a Satellite's position/orbit be calculated using only range measurements from ground stations?

This task is often done in a process known as Satellite Laser Ranging (SLR). SLR stations (of known coordinates) track satellites, recording range measurements to the satellite at known times. I would ...
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### Orbital period and velocity around a Kerr black hole relative to fixed stars

I've been trying to make progress on some of the smaller pieces of this question about the environment around a Kerr black hole. In order to calculate the effects of special relativistic Doppler shift ...
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### Why can't we detect the Earth's orbital motion when looking at the sky and stars?

After I read that speed of earth orbit around the sun is 30 km/s, I looked at sky and I didn't notice any change when compared to the start location. 30 km/s can be converted to (30 * 60 ) km/minute ...
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### How to calculate the mass of the orbiting body given only its orbital information

A question asks the following: Using Newton’s Law of Gravity, show that the mass of a planet can be written: $$M = \frac{4\pi^2a^3}{ GP^3}$$ where $a$ is the semi-major axis and $P$ is the orbital ...
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### How does the total change in energy being negative indicate the direction of the Force?

To be more precise consider the following situation: Suppose a satellite is orbiting at a distance of $r_1$ from the centre of the earth. After some time, rockets are fired such that the new distance ...
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### Methods for handling close approaches in $N$-body simulations

In direct gravitational $N$-body simulations, what are the preferred methods for handling close approaches between bodies in order to preserve the accuracy of the evolution of the system?
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### Orbiting in space (free fall) and centripetal force?

So basically astronauts are weightless b/c they are free falling. But to get to that state they need to be moving real fast. So why doesn't that speed along with the centripetal force affect them? I ...
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### Deriving Stumpff functions for parabolic and hyperbolic orbits

I would like to know how I can derive Stumpff functions analytically for hyperbolic and parabolic orbits? It would be nice if you could tell me where I can read about it. Thanks, KS
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### Can a satellite be put into orbit such that it will always remain directly over a city? [duplicate]

Isn't it possible if we just set it high enough so that it's angular speed matches with the earth's? I think that the city must be on the equator to make this happen. Am I correct? Please can anyone ...
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### Can a satellite remain directly over a city?

Is it possible to put an artificial satellite into an orbit in such a way that it will always remain direct over a city (I mean at any specific place)?
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### Calculating true anomaly of a hyperbolic trajectory from time

I'm creating a simulation for orbiting bodies with my primary challenge being calculating the true anomaly of a trajectory with respect to time. I have figured out circular, elliptical, and parabolic ...
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### Is Keplers First Law a consequence of the conservation of angular momentum?

It would seem that once you have deduced that the angular momentum is conserved then you can deduce: $r^2\dot{\theta}=h$ is constant Combining this with the radial equation of motion then yeilds a ...
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### Change in energy during orbital decay

Suppose we have a planet orbiting a star and the planet radiates away some amount of energy $\Delta E$. I want to find by how much the orbit decays (i.e the change in orbital radius). One way to do ...
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### Setting up initial conditions of parabolic orbits, centre of mass frame

I am writing a simulation of 2 bodies in coplanar parabolic orbits in their centre of mass frame (in C++) and am having difficulties setting up the initial conditions for the velocities. The total ...
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### How do you explain Kepler's third law in general terms without complex math?

I understand the first law-elliptical orbits, and the second-equal area in same time, but I need help with the third one. Note that I am not in an AP course or taking calculus at the moment so simple ...
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### Do gravitational vawes deplete energy even if there's nothing they can affect?

I've read multiple times that one of consequences of gravitational waves being a thing is, that they make any orbit unstable. As long as the two or bodies orbit around each other, they create ...
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### What is the reason for Earth's rotation and revolution?

Is it because of the gravitational effect of the other planets and the sun then why do the other planets rotate and revolve too? And well does the Sun rotate and revolve too?
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### Why can't we put an object anywhere in the earth's orbit around the sun instead of Lagrangian points?

If we place an object in the earth's orbit around the sun, it should have the same orbital period right? For example, what would be the behavior of an object in orbit at point A1? It is at the ...
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### What is the angular distance between Ptolemaic perigees of Mercury?

In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that The complicated [Ptolemaic] model of Mercury has the curious ...