What is Orbits: Definition and 497 Discussions

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.
For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understanding of the exact mechanics of orbital motion.

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  1. m4r35n357

    I Explore Black Hole Orbits with My Kerr Orbit Simulator on YouTube

    Now my Kerr orbit simulator is pretty much feature complete, I have started to look at producing videos . . . I have just started a channel on YouTube to accumulate some of the more interesting examples. Aside from creating the simulation, the most difficult part was to generate useful initial...
  2. i_hate_math

    Satellites Orbits and Energy Problem

    Homework Statement Two small spaceships, each with mass m = 2000 kg, are in the circular Earth orbit of the figure, at an altitude h of 440 km. Igor, the commander of one of the ships, arrives at any fixed point in the orbit 81.0 s ahead of Picard, the commander of the other ship. What are the...
  3. P

    B Understanding Gravity & Orbits in Light of Relativity

    I've been re-reading Hawking's Brief book (for the fourth time :-) and trying to understand a bit more. He discusses how General Relativity tell us that the planets don't orbit due to gravity, but due to the bending of space-time by mass/energy. That in fact, they are actually following a...
  4. K

    B Why the Earth orbits around the Sun

    As far as I know, the Earth orbits around the Sun because of the centripetal force , and as far as I know, friction and gravitation from other planets should affect the circular motion of the Earth and so the path of the Earth should not be necessary that perfect. In addition, there must be...
  5. T

    I Angular Momenta and Actions of Orbits

    Consider a tiny planet orbiting a massive star. If the value of the planet's angular momentum (w.r.t. to star) is fixed, does the action of the planet's orbit depend on the eccentricity of the orbit?
  6. Alltimegreat1

    Direction of stars' orbits around galactic center

    Do all stars in the Milky Way orbit the galactic center in approximately the same direction? Also, toward which Zodiac constellation is the Sun moving in its orbit?
  7. RoboNerd

    Question on Orbits and Kepler/Uni. Grav. Laws

    Homework Statement The picture has the problem question. OK. When the moon is at point B, the distance from the moon to the center of the planet is most nearly: A) (1/25) * rA B) (1/5) * rA C) (1/ sqrt(5) ) * rA D) rA E) sqrt(5) * rA. Homework Equations Newton's law of gravitation...
  8. Alltimegreat1

    B Orbit Likelihood: The Odds of Objects Falling into Stable Orbits Explained

    How likely or unlikely is it for a passing object to fall into a stable orbit of another object? For example, if an Earth-sized rogue planet came near the sun, would the odds be something like 10 million to 1 that it would fall into a stable orbit?
  9. M

    MHB Number of Orbits: Showing Equality of Group G and G_a

    Hey! :o Let the finite group $G$ act transitively on the set $\Omega$. Then the action of $G$ and on $\Omega\times\Omega$ is defined as follows $(a,b)\cdot x=(a\cdot x, b\cdot x)$. Let $a\in \Omega$. Show that the number of orbits of $G$ on $\Omega\times\Omega$ is equal to the number of...
  10. Jorrie

    Perihelion Shift in Near-Circular Orbits: 6πm/a + Higher Order Terms

    The full power series for the Schwarzschild portion of perihelion shift is given in Mathpages as: where L = a(1-\epsilon^2), a the semi-minor axis and \epsilon the eccentricity. This implies that as \epsilon tends to zero, the perihelion shift tends to a non-vanishing 6\pi m/a + some much...
  11. Z

    Question about Orbits of Moon/Earth around Sun

    How, exactly, is the moon able to orbit the Earth while at the same time moving with Earth's orbit of the Sun? I understand that the Earth/Moon both have the same accelerations caused by the Sun's gravity, but accelerations are not additive - only forces. At any time, the moon will be pulled by...
  12. Geoff Pollock

    Acceleration in an Elliptical Orbit

    So let's say you are on an orbital satellite in an elliptical orbit around our planet Earth, meaning that the at one point in the orbit you are going faster, due to the gravitational pull of the planet. Would you feel the acceleration in space due to the shape of the orbit?
  13. D

    Kepler's third law for elliptical orbits

    Kepler's third law states T^2=(4pi^2/GM) x r^3 for CIRCULAR orbits. My question is, in the derivation for this equation ma=GMm/r^2 why can centripetal acceleration be used to replace a at m(v^2/r)=GMm/r^2 yielding v^2/r=GM/r^2 when the orbit is not circular. Planets have elliptical orbits so why...
  14. A

    What causes orbits to change over time?

    There are two examples: A planet rotating around a star and a spacecraft maneuvering through space. Let's assume that solar radiation has no affect on the spacecraft and the spacecraft is not bumping into any stuff, and niether is the planet; and no other gravitational sources are involved...
  15. Alltimegreat1

    Galactic Orbit Variations: Impact on Night Sky View

    I just read that our solar system takes 225 million years to orbit the center of the galaxy. Is it possible that the other nearby stars in the Milky Way are orbiting faster or slower or have a more or a less circular orbit than does our Sun? If so, would the stars in the night sky as viewed...
  16. Stephanus

    Orbits in Universe: Milky Way, Sun, Moon & More

    Dear PF Forum, Lunar Satelite orbits the moon, The moon orbits the earth, The Earth orbits the sun, I know that some of you know about this picture You might want to tell me. "No Steven, the Sun also orbits the earth" But for all practical purpose, we'd say that the earth orbits the sun. So...
  17. F

    Do We Agree on How Orbits Work?

    Would you guys agree with these websites on how orbits work? http://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-orbit-58.htmlhttp://www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-causes-an-orbit.html
  18. H Smith 94

    Verlet algorithm: Why am I getting this output?

    Hi! I am currently trying to write a code in C to simulate the orbit of planets around the Sun in the solar system. I am using the velocity Verlet approach and finding that my code produces no acceleration in the ##y##-direction (aside from for ##t_n = 0##,) and that the planet just flies off...
  19. 450AHX

    How can I generate an elliptical orbit using only position and velocity data?

    Hi. I'm writing a simulation of (an approximation of) the solar system. So far I've been able to translate the Wikipedia article on Kepler's laws to a function that uses a description of an elliptical orbit (eccentricity, periapsis, known position in time) to return a position when passed an...
  20. T

    Concerning SOHO's orbit, and its corrections.

    Hi, I've read that SOHO (SOlar and Heliospheric Observatory) is orbiting around the L1 point. I remember this point being unstable (that is, that something in orbit will diverge from stability). How are the corrections made for this orbit ? Does it really cost a tiny amount of fuel, or is the...
  21. E

    Maxwell's theory and electrons in orbits

    Homework Statement Using Maxwell's theory of EM waves, show that an electron while revolving in Bohr's orbit does not radiate any energy. It radiates energy only when it jumps from a higher energy orbit to a lower energy orbit. Homework Equations...
  22. Warfen

    Gravitational Time Dilation & Orbits of Objects

    For example if there were two objects orbiting each other and one was much heavier than the other, for instance a dwarf star and a neutron star. Would the lighter object have a greater gravitational pull than it's mass would say it should because it's pull was operating longer on the heavier...
  23. C

    Trouble understanding angular momentum in relation to orbits

    Hi, Two questions. 1) I'm having trouble understanding the stability of the stable Lagrangian points (L_4 and L_5); Wikipedia explains that if an object in the L_4 or L_5 of a planet is pushed closer towards the common center of gravity of the Sun and the planet, the increased speed that comes...
  24. D

    Algebra, find orbits and stabilizers

    Hello I have the solution of a problem and I don't understand it 1. Homework Statement We know that every subgroup L<S10 acts on [1, 10] := {1, 2,..., 10} by the formula π • i = π(i). Consider L the subgroup of S10 generated by the permutation p = (1, 2, 3, 4)(4, 5)(8, 9, 10). Find the orbit...
  25. J

    Periods and Motion of Orbits, CM and Relative Motions

    Homework Statement (a) Using elementary Newtonian mechanics find the period of a mass m1 in a circular orbit of radius r around a fixed mass m2 (solved, but placing for context). (b) Using the separation into CM and relative motions, find the corresponding period for the case that m2 is not...
  26. Q

    Planck's constant in planetary orbits

    The question is: If quantum mechanics were detectable in planetary orbits, how much larger than the currently accepted value would Plancks constant need to be? Relevant equations ΔxΔpx ≥ħ/2 p=mv Earth-Sun dist 1.496E11 Earth orbit speed 28,900ms^-1 Earth mass 5.972E24 kg The attempt at a...
  27. I

    How did planets get their Orbits?

    An orbit is a fixed path in space around a mass. Once an object gets into an orbit, it would stay there until an outside force pulled it out. Thus, there are only two ways to be in an orbit. Either an object was already in orbit, or it inserted itself into orbit. Since a planet cannot...
  28. skepticwulf

    Empty space in atoms vs orbits

    We often read that atoms are mostly empty space. A common example is given as, if the atom was a big as a football stadium the nucleus would be as big as a tennis ball on the center and nearest electrons circling around at far side of seats or something like that. How does this reconcile with...
  29. Quotidian

    Earth-Like Planet orbits Sun-Like Star

    That, anyway, is the headline in today's news, regarding the interesting discovery announced by NASA overnight of the planet dubbed Kepler-452b. As I understand it, the properties of the planet are inferred from spectral analysis of its effects on the light from the star which it orbits...
  30. R

    Intersecting Orbits of Binary Stars: A Visual Guide

    Is it possible that 2 stars in a binary system to intersect their orbits like in this picture? ( the orbital plane is perpendicular to the line of sight)
  31. D

    Are Newton's Laws Still Valid Near Black Hole Orbits?

    Classical calculated with Newton the escape speed is r = 2G.M/v2. With v = c that would be the same as the Scharzschild radius calculated with GR. Does that mean that Newton laws are still valid at (or just outside) this radius?
  32. T

    Exploring the Reliability of Euler Method for Orbital Gravity Equations

    Hello everyone, I am curious as to if it is possible to use the Euler Method to solve the gravity differential equations? Would the approximations quickly diverge to inaccurate solutions, or would it stay relatively reliable? Thanks
  33. Hansa

    How did Kepler derive his laws WITHOUT law of gravitation?

    How did Kepler derive his laws of Planetary Motion without knowing about Newton's law of gravitation? Specifically, the first law of planetary motion which says that planets follow elliptical paths - how did he figure that out without the knowledge of the gravitational pull of the sun? Was it...
  34. RisingSun361

    Question about Kepler's 1st law and barycentric orbits

    Kepler's 1st law states, "All planets move about the sun in elliptical orbits, having the sun as one of the foci". But the orbit must also be barycentric. So, technically speaking, is the center of mass of the system actually at the focus, rather than the sun? And the sun itself orbits this...
  35. P

    Orbital Rendezvous and Mission Control Involvement

    Can someone please give a step by step explanation of an orbital rendezvous by a spacecraft for a target that is orbiting the body it launched from? And if possible, can you explain how mission control is involved and what part computers play? When the RCS is active is it changing the...
  36. D

    Elliptical Orbits In The Schwarzschild Metric

    I was just wondering how you would go about calculating the proper time for an observer following a freely falling elliptical orbit in a Schwarzschild metric. I am happy with how to calculate the proper time for a circular orbit and was wondering whether if you had two observers start and end...
  37. gulfcoastfella

    Predicting orbits and masses of as-yet-unknown bodies

    I read an article on Phys.org (The Strange Case of the Missing Dwarf), and as I'm in the middle of reading and studying Hamiltonian Dynamics, the article made me wonder how the unexplained orbits of existing bodies are used to determine the orbits and masses of as-yet-undiscovered bodies. It...
  38. G

    Minimum Orbital Radius Around Black Holes

    Hi there, I was reading one of my textbooks and I had a thought. For a black hole, there is minimum orbiting radius of ##R_{min}=3R_s## where ##R_s## is the Schwarzschild Radius. This minimum orbit is created by the fact that in order to obtain an orbit of that radius around a black hole, you...
  39. G

    Relationship between characteristic energy and delta-v

    Firstly, apologies if this is in the wrong thread. I'm currently writing a presentation on the physics of getting a spacecraft from Earth to Mars in the near future. In my research I've come up against Porkchop plots which seem to plot contours of equal characteristic energy so you can find...
  40. 2

    Confused about binary star systems?

    I was thinking about the motion of two stars in a binary star system, but there is something I cannot quite figure out. Suppose you have a binary star system with two stars masses m1 and m2 with m2>m1 so that m2 is closer to the centre of mass of the system. Then when the two stars are as far...
  41. L

    Structure of orbits at a tornado, whrilwind, etc.

    Any sites showing the whole structure of direct orbits of air molecules inside and outside of any type of turbine? By "direct" orbits, I mean between the two successive clashes of each molecule with other molecules.
  42. starchaser2020

    Calculating Delta V for Orbit Change

    A satellite changes its orbit inclined 66° at 260.0 km altitude to a polar orbit at the same altitude. What Delta V was required? ... I am stuck. do I figure it out using: DeltaV1 = |V_transfer at orbit 1 - V_orbit 1| and DeltaV2 = |V_transfer at orbit 2 - V_orbit 2| or is there another...
  43. starchaser2020

    What is the K.E. of the satellite?

    A satellite has been placed in a circular, sun-synchronous orbit at an altitude of 1300.0 km. The satellite has a mass of 5,000.0 kg. What is the K.E. of the satellite? I know K=(1/2)mv^2 ... but I have no idea where to go from here. I Know I am over-thinking this. So any help would be greatly...
  44. Nathanael

    Do tidal forces slowly make orbits more circular?

    I don't understand, how can tidal forces make the orbits more circular? Perhaps it has something to do with the fact that in elliptical orbits (unlike in circular orbits) the velocity is not always perpendicular to the acceleration? Or maybe it does not have to do with the tidal forces from the...
  45. N

    Relativistic Orbits: Effects of Mass Increase & Length Contraction

    Suppose an observer flies through our solar system at ##v \approx c## relative to the Sun, such that he sees each planet's (and the sun's) mass as greatly increased. What happens to the orbits of the planets? Since he sees the center of mass of the solar system as flying past him at ##v \approx...
  46. J

    Planetary Orbits & Orbital Velocity

    Hi pf, please could someone explain why the orbital velocity increases as you get closer to the sun. I treated the situation like circular motion and did a load of calculations. I calculated the orbital velocity of all 8 planets and then the force between each of the eight planets and the sun. I...
  47. D

    How does Rosetta stay in orbit?

    News stories make it sound like Rosetta is orbiting the comet. But presumably the comet's gravity is negligible, which means that orbiting it would require continuous acceleration (and therefore continuous use of energy) in order for Rosetta's motion to conform to a circle/ellipse, rather than...
  48. S

    Asteroid Orbits: Finding r with Kepler's Laws

    Homework Statement An asteroid of mass m is in circular orbit of radius r around the sun with speed v.It has an impact with another asteroid of mass M and is kicked into a new circular orbit with a speed 1.5v.What is the radius of the new orbit in terms r?[/B]Homework Equations (v1)^2/(v2)^2 =...
  49. M

    What is the significance of the foci in gravitational orbits?

    hey everyone, this is a qualitative question on gravitational orbits: I was going through questions in which the trajectory of the orbiting body is determined based upon the eccentricity of the orbit, e.g. 0<Ecc<1, ellipses, Ecc=1, parabola, Ecc>1, hyperbola. I did the math and found out what...
  50. C

    Strange behavior for orbits of inverse cube forces and higher?

    After working a homework assignment which required sketching effective potential energy for the gravitational/coloumb forces, I went and looked at a few effective potentials for inverse cube and inverse quartic (not sure if this is the right word; 1/r^4 force) forces, with inverse square and...
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