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

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33
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2answers
1k views

Why are our planets in the solar system all on the same disc/plane/layer?

I always see pictures of the solar system where our sun is in the middle and the planets surround the sun. All these planets move on orbits on the same layer. Why?
10
votes
12answers
4k views

Why do we say that the earth moves around the sun?

In history we are taught that the Catholic Church was wrong, because the Sun does not move around the Earth, instead the Earth moves around the Sun. But then in physics we learn that movement is ...
4
votes
1answer
479 views

Radial fall in a Newtonian gravitational field [duplicate]

Suppose an object of mass $m$ starts at rest at a radial distance $ r_0$ from a perfectly spherical mass $M$ (where $m << M$), $r_0 > R =$ radius of $M$. Can we analytically determine when ...
15
votes
4answers
3k views

Are tidal power plants slowing down Earth's rotation?

Are tidal power plants slowing down Earth's rotation to the speed of the orbiting moon? (1 rotation per 28 cca days) Are they vice versa increasing the speed of moon orbiting by generating some ...
8
votes
1answer
277 views

What are common methods for calculating the time dependency of elliptical orbit?

After playing a game called "Kerbal Space Program" I got interested in orbital mechanics and started messing with simplified calculations to determine $\Delta v$ requirements. In which I compared two ...
9
votes
3answers
562 views

Questions about the Solar System

Most images you see of the solar system are 2D and all planets orbit in the same plane. In a 3D view, are really all planets orbiting in similar planes? Is there a reason for this? I'd expect that ...
15
votes
4answers
4k views

What did general relativity clarify about Mercury?

I frequently hear that Kepler, using his equations of orbital motion, could predict the orbits of all the planets to a high degree of accuracy -- except Mercury. I've heard that mercury's motion ...
7
votes
10answers
1k views

Is the distance between the sun and the earth increasing?

M = mass of the sun m = mass of the earth r = distance between the earth and the sun The sun is converting mass into energy by nuclear fusion. $F = \frac{GMm}{r^2} = \frac{mv^2}{r} \rightarrow r ...
4
votes
1answer
413 views

How does an object falling into a plain Schwarschild black hole appear from near the black hole?

I know that when viewed from infinity (or from a very large distance from the black hole event horizon), an object that falls into the black hole will appear to slow down and will become more and more ...
5
votes
4answers
416 views

Are galactic stars spiraling inwards?

Are the stars in our galaxy spiraling inwards towards the center, or are they in a permanent orbit? And if we are heading towards the center then what is the rate of this process? I started ...
3
votes
1answer
591 views

About binary stars and calculating velocity, period and radius of their orbit

I saw somewhere about being able to measure the velocity, period and radius of a binary star orbit by looking at red shift and blue shift. I understand it but can someone give me an example of ...
3
votes
4answers
1k views

Does mass affect speed of orbit at a certain distance?

Does the mass of both the parent object, and the child object affect the speed at which the child object orbits the parent object? I thought it didn't (something like $T^2 \approx R^3$) until I saw ...
21
votes
5answers
2k views

What symmetry causes the Runge-Lenz vector to be conserved?

Noether's theorem relates symmetries to conserved quantities. For a central potential $V \propto \frac{1}{r}$, the Laplace-Runge-Lenz vector is conserved. What is the symmetry associated with the ...
9
votes
3answers
2k views

Gravity in other dimensions than 3 and stable orbits

I have heard from here that stable orbits (ones that require a large amount of force to push it significantly out of it's elliptical path) can only exist in a three spatial dimensions because gravity ...
7
votes
2answers
460 views

What happens to orbits at small radii in general relativity?

I know that (most) elliptic orbits precess due to the math of general relativity, like this: source: http://en.wikipedia.org/wiki/Two-body_problem_in_general_relativity I also know that something ...
5
votes
1answer
386 views

When and how were relative distances to the planets first measured?

I understand that the absolute distance to a planet can be measured using earth-baseline (e.g., diurnal) parallax, and that the first reasonably accurate such measurement was made for Mars by Cassini ...
0
votes
3answers
886 views

Uniform Circular Motion

Why does the object not go inward, into the circle if the acceleration is inward? I think its because the velocity to outward? So they sort of cancel each other out? But if the speed is kept ...
21
votes
6answers
3k views

Could there be a star orbiting around a planet?

I wonder if there ever could be a star (really small) which may orbit around a planet (really big)?
14
votes
5answers
4k views

Why do we always see the same side of the Moon? [duplicate]

I am puzzled why we always see the same side of the Moon even though it is rotating around its own axis apart from revolving around the earth. Shouldn't this only be possible if the Moon is not ...
13
votes
1answer
1k views

When will the Moon reach escape velocity?

From what I know, the Moon is accelerating away from the Earth. Do we know when it will reach escape velocity? How do we calculate this?
7
votes
3answers
231 views

What exactly is the microgravity field in orbit?

The ISS and other objects in orbit still experience small acceleration outside from the perfect line of orbit (of the system CM). For instance, two objects in the ISS that are let to be at rest will ...
2
votes
2answers
344 views

Expression for distance of closest approach in Schwarzschild Geodesics

The Wikipedia article Two-body problem in General Relativity uses two length-scale variables, $a$ and $b$, to simplify the math. For some information about these, consider these statements from the ...
2
votes
3answers
230 views

Can a photon be made to orbit a known (or undiscovered theoretical) body?

Can a photon through some process be made to orbit a celestial or any other object? Two follow-up questions. Can this orbit be described as the photon crossing its own path. Will this ...
2
votes
2answers
897 views

Why is the center-of-mass of 2 bodies at the focus of their elliptical orbits?

Why is the center-of-mass of 2 bodies (which interact only via Newtonian gravity) located at a focus of each of the elliptical orbits? I know that when there are no external forces, the center of ...
2
votes
1answer
2k views

What are the temperatures of objects in Low Earth Orbit (LEO)?

What is the temperature of objects in Low Earth Orbit? Consider LEO to be 600km to 800km.
-1
votes
4answers
183 views

How do electrons get the energy to jump from one orbital to the next when in stationary orbits the electron does not radiate energy

My Question is how do electrons get energy/lose energy to jump up or down an orbital as in a stationary orbit they do not gain energy and their energy is finite?
11
votes
4answers
1k views

Is Feynman's explanation of how the moon stays in orbit wrong?

Yesterday, I understood what it means to say that the moon is constantly falling (from a lecture by Richard Feynman). In the picture below there is the moon in green which is orbiting the earth in ...
9
votes
6answers
17k views

Gravity on the International Space Station

We created a table in my physics class which contained the strength of gravity on different planet and objects in space. At altitude 0(earth), the gravitational strength is 100%. On the moon at ...
8
votes
2answers
227 views

Intuitive explanation of why orbits are closed?

Yesterday my brother asked me how orbits work. Suppose for the sake of the question that you are trying to put a rocket in orbit around the Earth. I explained that orbiting is essentially being in ...
12
votes
6answers
20k views

Is Melancholia's orbit impossible?

In the 2011 movie Melancholia, a planet, also called Melancholia, enters the solar system and hits the Earth. I want to leave aside the (also unreasonable) aspect that planet "hides behind the Sun" ...
12
votes
6answers
3k views

Why are the orbits of planets in the Solar System nearly circular?

Except for Mercury, the planets in the Solar System have very small eccentricities. Is this property special to the Solar System? Wikipedia states: Most exoplanets with orbital periods of 20 ...
1
vote
1answer
529 views

Why does the moon or the earth revolve anti-clockwise?

The question is very simple: Why does the moon or the earth or any another planet revolve anti-clockwise? And can any planet (or satellite) revolve clockwise? What is the physical law for this ...
5
votes
3answers
653 views

Binary Star system with one star stationary?

Can a Binary Star system be possible where in one star is stationary and the other star revolves around it? (Just like a planet revolving a star. i.e planets in the system and the star revolving ...
4
votes
1answer
326 views

What is the precise definition of Gravitational Sphere of Influence (SOI)?

I am trying to understand the gravitational sphere of influence (SOI), but all I get by searching is the formula that you can find on Wikipedia, that is $$ r_{SOI} = a \left( \frac{m}{M} ...
3
votes
1answer
87 views

Why doesn't this equation for orbital motion change with position in the orbit?

The question and answer are on pg.8-10 of this PDF: At first, I went through it, thinking nothing of it. But then, I wondered: "What if we picked a final state in which the space junk was NOT at ...
3
votes
4answers
2k views

Can a balloon float into space? (+orbital velocity)

After watching the recent "space jump" a question arose. Why can a balloon not float into space? Can one be made/designed to do this? Next, everything in orbit is falling back to earth. It only ...
6
votes
2answers
247 views

Why is there this asymmetry between the two foci of an orbital ellipse?

Why does the Earth revolve with the Sun at one of its foci? Does the other focus do nothing? Why is there this asymmetry in our solar system?
4
votes
2answers
369 views

Calculating Orbital Vectors in the Future

For the 2D space simulator that I am writing (please note, it is not at all homework), I require formulas that will give me the location and velocity of a spaceship, relative to the parent celestial ...
4
votes
1answer
246 views

Can you tell just from its gravity whether the Moon is above or below you?

If you are on a place of Earth where the Moon is currently directly above or directly below you, you experience a slightly reduced gravitational acceleration because of Moon's gravity. This is what ...
3
votes
2answers
621 views

When is the right ascension of the mean sun 0?

I understand that the right ascension of the mean sun changes (at least over a specified period) by a constant rate, but where is it zero? I had naively assumed that it would be zero at the most ...
3
votes
1answer
342 views

How do I calculate the time it would take for a space craft launching from earth to reach another planet?

I am making a matlab program the my final project for my programming class in college. I have chosen this problem, but I am bashing my head against the wall trying to figure out the equations and how ...
3
votes
3answers
441 views

Orbital mechanics of Dragon's Egg

In the novel Dragon's Egg, the human crew use one asteroid to swing other asteroids in place to counter the gravity of the neutron star. I understood that it was similar to a gravity sling shot, but I ...
2
votes
1answer
110 views

Stable and Unstable Orbital Resonance

I was wondering if anyone can show me why some orbital resonances are unstable. For example in the asteroid belt there is a depleted distribution at 3:1 resonance with jupiter. What is the cause of ...
2
votes
2answers
395 views

Does the length of the sidereal day vary systematically?

I'm confused about some properties of the sidereal day, in particular whether its duration varies systematically over the course of the year.1 It seems to me that that must be the case, but the ...
2
votes
1answer
536 views

How did Copernicus establish the relative distance to the superior planets?

I understand that the relative distances to the planets had been calculated using various methods since ancient times, and, in particular, that the assumptions of the Copernican model of the Solar ...
1
vote
1answer
84 views

Perihelion Advance in curve space

I've been doing some work that involves particle's motion subjected to central forces. I was trying to compute the perihelion advance of the particle's path. For that I've been following this ...
1
vote
2answers
338 views

Semi-major axis and ellipticity of a binary system?

In the image below (source at bottom), it seems to be suggesting that \begin{equation} a = a_{1} + a_{2}, \hspace{8cm}(1) \end{equation} where $a_{1}$ and $a_{2}$ are the semi-major axis of the ...
17
votes
2answers
217 views

Why don't stars in globular clusters all orbit in the same plane?

Globular clusters like Omega Centauri certainly don't seem to be very coplanar at all. In other words, why doesn't the explanation at Why are our planets in the solar system all on the same ...
10
votes
1answer
382 views

Mars just collided with Earth! A question of eccentricity

One of the standard theories behind the formation of our Moon is the giant impact hypothesis, according to which Earth was struck by a Mars-sized body (about $10\%$ the mass of Earth) early in its ...
6
votes
2answers
310 views

Are there planetary systems where the planes of orbits vary greatly?

Inspired by this question, are there any known planetary systems with largely varying planes of orbit? For example a system where two planets have perpendicular planes?