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. J

    Logarithmic spiral photon orbits

    Hello, It has been said if a photon crosses the event horizon of a black hole it will have a spiral orbit; The spiral is Archimedes r = r_{i}+r_{0}\theta^2 There is one such example in "Introduction to tensor calculus, relativity and cosmology" by D F Lawden on page 165 Is it possible...
  2. S

    Hydrogen orbits, magnetic field, orbit-spin interaction

    Homework Statement In different (scientific) sites I find different values for MF of H-1 ranging from 0.3 to 0.6 Tesla. Isn't there a generally acknowledged value? what about H-2 and H-3 ? The Attempt at a Solution using the general formula I get 1/ 8 tesla, that formula it not valid...
  3. Philosophaie

    Planetary Orbits calculated from the Metric

    I am learning about General Relativity. The planetary orbits can be calculated with more precision especially Mercury. I am stuck on how to get from the Schwarzschild Metric: a four variable Differential Equation to a radius(r,theta,phi,t) and velocity(r,theta,phi,t) of a single planet...
  4. R

    Function for orbits based on time.

    Okay, I am trying to find a formula for the position of two bodies (or more) in space based on the initial velocity and time. I'm trying to integrate the equation for gravitational acceleration to find the velocity equation, however, the radius is changing, and the degree (theta) is also...
  5. stevmg

    Elliptical Orbits (Using Newton's Model)

    1) Is it theoretically possible in a universe of two planetary objects - a Sun in a fixed position and a planet of any other finite mass, for that planet to orbit the sun in a perfectly circular orbit (not an ellipse?) 2) Are the elliptical (or near elliptical) orbits that occur in the real...
  6. stevmg

    Explaining the Heisenberg Uncertainty Principle and Electron Orbits

    It is stated that electrons orbit the nuclei of atoms not as particles. By the Heisenberg Uncertainty Principle (whatever that is) one cannot pinpoint their actual location and one cannot track the motion of an electron as it orbits the nucleus. What is that all about? Please use 10th...
  7. R

    Closed orbits in hydrogen when exposed to vertical electric field

    Hi. I am trying to find the classical turning points in semi-parabolic coordinates for the hydrogen atom when an electric field is being applied to it in the y-axis. I am reading an article for those who are interested called Classical, semiclassical, and quantum dynamics in the lithium Stark...
  8. N

    Question about mechanical energy and orbits

    I was watching something on elliptical orbits. Early on, I saw something that really bugged me and I can't continue until I figure out what it's about: Mechanical Energy = Kinetic Energy + Potential Energy I know that KE = 1/2*mv^2, which makes sense and I know why I know that PE = mgh =...
  9. L

    Pictures of electron etc orbits

    Pictures of "electron etc orbits" http://www.sciencephoto.com/images/download_lo_res.html?id=651380013 Are they photographs and the "orbits" happened at some distance form the lens? Then, how much is that distance? What are the actual sizes of these shapings? I.e. how many milimetres is...
  10. L

    Investigating Acceleration and Orbits in Rindler Spacetime

    On page 36 of these notes: http://arxiv.org/PS_cache/gr-qc/pdf/9707/9707012v1.pdf we are given a proof of the claim at the bottom of p35. However, this proof doesn't actually seem to do anything! All he does in the proof is shows what the acceleration is - he doesn't make any connection with...
  11. L

    Elliptical Orbit: Determine Foci & Missile Path

    Given an elliptical orbit, if I know all parameters of the ellipse, is it possible to determine in which of the two foci is the star? To be more precise, if I put into orbit a missile from earth, it will reach first the perihelion and then aphelion or vice versa? How can I know?
  12. C

    Stable orbits for hot Jupiters?

    Would it seem reasonable that so-called ‘hot jupiters’ are in resonance i.e. have a stable orbit? If one utilized our stellar system as a simulation, with the addition of a hot jupiter, then what would the resonance be? Would it be calculated as non integral? Then if our cold gas giant were...
  13. B

    Acceleration in elliptical orbits ?

    How is acceleration between aphelion and perihelion calculated? Which equation can be used?
  14. C

    Approximating Ellipse Orbits with Newton's Law

    How do you approximate the ellipse of an object's orbit using Newton's law of universal gravitation? I'm working on a 2D space game and that's pretty much the only physics I use, so no other forces to consider.
  15. P

    Equations of Motion for 'Perturbed' Or 'Oblique Incidence' Orbits?

    Hi, I've been doing a Q where particles undergo circular/near-circular motion in an electric field. The electric field varies as 1/r. With the first particle, they set it off tangentially to the field lines, so it undergoes circular motion. With the second particle, they set it off at a...
  16. J

    The Basics Regarding : Planetary Orbits and Whatnot

    Q: Why is it that objects in orbit around other objects, tend to do that in elliptical patterns, and not circular patterns? I can picture objects of great mass, planets and stars warping the fabric of space time, and how moons and whatnot get caught spinning in the orbit. But can't wrap my head...
  17. S

    Plotting Planets Orbits around Sun using Schwarzchild Metric

    Hello, I'm currently studying general relatively and am trying to plot orbits of planets around the sun using the schwarzchild metric. I've worked out the geodesic equations, working with c=1 to simplify things, and written a MATLAB script to plot trajectories, but I'm struggling to work out...
  18. F

    Periodic Orbits on Cylinder: Bendixson's Theorem

    Homework Statement Show that the following vector field on the cylinder has a periodic orbit, v' = -v Θ' = 1 Homework Equations Bendixson's theorem: Suppose D is a simply connected open subset of R^2. If the expression div(f,g) = ∂f/∂x + ∂g/∂y is not identically zero...
  19. L

    What are the shapes of orbits that exist in our solar system

    Can anyone help me please? Are they all elliptic or just some? I need to know for planets, comets, moons and satellites All help greatly appreciated.
  20. O

    Optimizing Orbital Trajectories for Efficient Mars Encounter

    A space probe initially moving in a 1 AU circular orbit around the sun (i.e. moving with the earth). The aim is to put this space probe in an orbit that will encounter Mars, using the least possible expenditure of rocket fuel (energy). This orbit, it turns out, is one in which perihelion...
  21. S

    The eccentricity of binary stars' orbits

    Hi As two stars orbit their mutual center of mass in elliptical orbits, why are their eccentricity the same? And why is it the same as the one of reduced mass around center of mass? Thanks
  22. C

    E-Classifying Orbits: Learn How to Numerically Categorize Orbits

    Hello! I need help with this question: Name a way, in which different types of orbits are numerically categorized? (Hint: Starts with an "e")
  23. U

    This is the question which is asked in this content.

    I'm trying to derive the energy in an orbit and don't quite understand it (which makes remembering it pretty difficult for exams!) I've put parts of my notes relating to this below. My first problem is with the integration (2nd equation to 3rd equation). I've tried using integration by parts...
  24. E

    Calculate distance between two planets in elliptical orbits

    Homework Statement Two planets are orbiting the sun in elliptical orbits in the same plane. The orbit of planet Q has a semi-major axis of 64.8 AU and eccentricity of 0.445. Planet R has a semi-major axis of 42.5 AU and eccentricity of 0.825. The perihelion point of Planet R's orbit is...
  25. U

    Circular Orbits in SR: Force, mv^2/r, L Conservation

    In CM there is this equation of motion for ciruclar orbits: F=k/r^2=m*v^2/r, where k depends on the force involved. I know this gets complicated in GR, but is there a simple expression for circular orbits in SR, what happends to the m*v^2/r ? If the forces are only electromagnetic, does k/r^2...
  26. S

    Why Are Planetary Orbits Elliptical?

    Why are the orbits of planets revolving around a body(say the sun) elliptical rather than circular or any other shape? Please show the answer mathematically.
  27. N

    Calculating Time Interval of Two Earth Satellites in Circular Orbits

    Homework Statement Two satellites of the Earth move in a common plane along circular orbits , the radii being r and r-\Deltar ( \Deltar << r ). What is the time interval b/w their periodic approaches to each other over the min. distance . Take M to be the mass of the Earth M = 6 * 10 24 kg ...
  28. S

    Interpreting Gravitation: Orbits & Ellipticals

    *Has General Relativity got some interpretations saying planets and satellites don't act as single mass? *Also can it be that orbits of all orbiting bodies are elliptical or seem elliptical due to moving central body?
  29. S

    Circular Orbits and weightlessness

    Homework Statement A small projectile is launched parallel to the ground at height h = 1 m with sufficient speed to orbit a completely smooth, airless planet. A bug rides in a small hole inside the projectile. Is the bug weightless? Explain. The Attempt at a Solution I didnt understand...
  30. gttjohn

    Why do Planets have elliptical orbits ,AND

    why do Planets have elliptical orbits ,why do they just not have circular orbits ,I understand that the sun is like a bowling ball on a sheet of rubber and the planets in our solar system orbit the bowling ball as if i got a marble and rolled it onto the sheet of rubber but after a while the...
  31. M

    Energy difference between orbits?

    Homework Statement The space shuttle is in a 100 km-high circular orbit. It needs to reach a 610 km-high circular orbit to catch the Hubble Space Telescope for repairs. The shuttle's mass is 6.50×104 kg. How much energy is required to boost it to the new orbit? Me(mass of earth) = 5.98E24 =...
  32. P

    Three types of non-circular orbits

    Homework Statement Rank the three types of non-circular orbits in order of increasing total energy (kinetic plus potential): The Attempt at a Solution Based on the picture I am looking at it seems. In increasing order it looks like ellipse , parabola , then hyperbola, but I am not...
  33. K

    Understanding Orbital Mechanics: The Force Behind Planetary Motion

    Hello I was searching a community like this one and I am glad I found one. I have a question about the beginning of the universe. I am trying to make a simulation of big bang, as I know after the big bang enormous amount of matter scatter around and they started to combine and turn into...
  34. L

    Astrophysics: question about nearly resonant orbits

    astrophyscs: question about nearly resonant orbits Homework Statement are any planets in low-integer resonant or nearly resonant (within two or three percent) orbits Homework Equations p2/p1 The Attempt at a Solution ok suppose to find for the planets of 55cancri so like 55cancri b...
  35. M

    Astrometry and Elliptical orbits

    You can measure the distance to an object orbiting the sun using parallax, and you can determine its angular velocity by measuring its change in position over several hours or days. From this you can calculate its orbit... if it were circular. However, comets and asteroids follow elliptical...
  36. N

    Electron falling between two orbits produces certain wavelenght of light

    Homework Statement Between which two orbits of the Bohr hydrogen atom must an electron fall to produce light of wavelength 954.8 nm ? Homework Equations E = hv E = R(1/n1^2 - 1/n2^2) The Attempt at a Solution I've got it down to the differences in the reciprocals of the squares...
  37. L

    What Are Common Misconceptions in Understanding Circular Motion and Orbits?

    Ok I have 2 related questions Qns1 Homework Statement Two satellites, A and B, orbiting around Earth have the same kinetic energy. Satellite A has a larger mass than satellite B. Which of the following statements is false? A Satellite A has a larger period. B Satellite A has a...
  38. M

    How to find the orbits of a subgroup?

    Homework Statement Hi everyone. I have just joined the community, and I really appreciate your help. Here is what I'm struggling with: Assume a permutation group G generated by set S, i.e., G=<S>. Since S is given, we can easily find the orbit partition for G. Now assume the subgroup H of G...
  39. D

    Calculating Time for a Radio Pulse to Travel between Earth and Venus

    Hi I'm a bit confused, I hope you can help. The question is - In the course of their orbits, the distance between the Earth and Venus changes. The radii of the orbits of the two planets are 1.5 x 10e8 km and 1.1 x 10e8 km. If a radio pulse is transmitted from Earth towards Venus, calculate...
  40. D

    Circular Orbit of a Spy Satellite: Calculating Altitude and Acceleration

    1. A spy satellite is in circular orbit around earth. It makes one revolution in 6.00 h. (a) How high above the Earth's surface is the satellite? (b) What is the satellite's acceleration?
  41. T

    Physics circular motion, orbits, and gravity

    Homework Statement ics Consider identical twins named Bert and Ernie who are visiting a star named Alpha Sesame. Bert is at a distance r from the star while Ernie is located a distance 3r. Both Bert and Ernie are stationary (they are standing on platforms built by an alien super race) and...
  42. E

    Exploring Chaotic Orbits: Approximating Periodic Trajectories

    Consider a dynamic system with a periodic trajectory. Given an arbitrary duration T of time, does there exist a chaotic trajectory of a similar system which approximates the closed orbit for the duration T with a given accuracy? Chaotic orbits which I've seen so far...
  43. stevebd1

    What is the equation for stable orbits in Kerr metric?

    The equation for the surface gravity of a black hole in Kerr metric is- \kappa_\pm=\frac{r_\pm-r_\mp}{2(r_\pm^2+a^2)} where r+ is the outer event horizon- r_+=M+\sqrt(M^2-a^2), r- is the inner event horizon- r_-=M-\sqrt(M^2-a^2) and a is the spin parameter in metres- a=J/mc. An exact...
  44. S

    Orbits of the planets and centripetal acceleration

    [b]1. The table below lists the average distance from each planet to the Sun and the time each planet takes to make a complete orbit around the Sun (“Orbital period”). The orbits of all of the planets are roughly circular. Your job is to determine a relationship between the radius r of a...
  45. C

    Comparing Orbits and Orbitals: Similarities and Differences Explained

    Homework Statement describe one way in which orbits are similar and two ways in which they are different Homework Equations N/A The Attempt at a Solution the differences: first, the orbital is a 3-dimensional volume of space where the probability of finding some electron is very...
  46. B

    Understanding Atom Orbits: Calculating Lost Energy

    Once it was thought that electrons was orbiting nucleus almost like planet the Sun. But this could not be correct because then would the electron lose their energy and spiral into the core. My question is how such orbit energy lost can be calculated. This is not homework.
  47. B

    Calculating Energy, Angular Momentum & Period for Binary Stars in ZMF

    Homework Statement Two individual stars in a binary system (m1=mo, m2=2mo) are in circular orbit about their common centre of mass and are separated by a distance ro. At some stage, the more massive star explodes - resulting in the two stars having equal mass after the explosion...
  48. O

    Orbits of Particle Around a Black Hole using Effective Potential

    Homework Statement The possible orbit of a particle moving around a black hole can be described using the effective potential UGR(r) (in effect, potential energy per unit mass): UGR(r) = -GM/r + l2/2m2r2 - Rsl2/2m2r3 where the symbols have their usual meaning and in particular...
  49. T

    Planetary orbits in a Binary Star system.

    http://spaceflightnow.com/news/n0210/11planet/ This is the only discovered planetary orbit around a close binary star that I know about. I have some general questions about planetary orbits around or within close binary systems or even the further apart binary star formations or triples...
  50. A

    Find Smallest Eccentricity for Intersecting Orbits

    Homework Statement Two masses, m and 2m, orbit around their CM. If the orbits are circular, they don't intersect. But if they are very elliptical, they do. What is the smallest value of eccentricity for which they intersect? Homework Equations...
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