What is Orbit: Definition and 1000 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. Bob R

    B How GR Predicts Earth's Orbit Around Sun: Geodesic Path & Curvature

    How does GR predict the Earth's orbit around the sun? Newtonian mechanics predict a gravitational force that is a function of the two masses. Is the geodesic path of the Earth a function of both the sun's and Earth's curvature of space?
  2. C

    What is the object's orbital path shown in the image?

    Summary: orbital path of an object Good morning I would like to ask the members of this forum their opinion regarding the object, which path I present in the image. The x-axis is the azimuth (towards me, the observer), and the y-axis the altitude. So it goes up in the trajectory shown (from A...
  3. P

    Extra speed necessary to orbit at 970 km

    So using conservation of energy where v0 = 7000 m/s $$ K_{i} + U_{i} = K_{f} + U_{f} $$ $$\frac{1}{2}mv^{2}_{0} - \frac{GMm}{R} = \frac{1}{2}mv^{2} - \frac{GMm}{r}$$ where R = the radius of the Earth and r = the distance from Earth's center plus the height its orbiting $$v =...
  4. T

    Binary System in circular orbit: Separation distance between stars

    Distance is d=1/0.07 = 14.3 parsecs The Doppler shift of one star is, Δλ = 512 - 512.04 = -0.04 So the radical of the velocity of the star is = (-0.04/512) x (3.00 x 10^5 km/s) = 23.4km/s which is the same for both stars because they have the same mass. This is as far as I've got.
  5. T

    B Temperature regulation in Earth orbit

    If I had an object in an orbit around the Earth that I kept continually shaded from the sun, how cold would it get? Assuming the shade device was not physically connected to and was sufficiently far away from the object to not radiate any heat to it. And if I actively adjusted how much shade...
  6. S

    Effect of time dilation on a satellite

    I've got the start of a plot forming in my mind, and I'm wondering if it's likely to be supported by physics at all. My basic understanding: when astronauts go to the International Space Station, due to the speed at which it is travelling, time passes ever-so-slightly slower for them. This...
  7. T

    I Typo in elliptical orbit energy derivation?

    I'm reading through a derivation for the energy of a satellite in an elliptical orbit. Shouldn't EO-2 read as: ... and not as shown in the following?
  8. D

    Equation of motion for oscillations about a stable orbit

    Homework Statement A) By examining the effective potential energy find the radius at which a planet with angular momentum L can orbit the sun in a circular orbit with fixed r (I have done this already) B) Show that the orbit is stable in the sense that a small radial nudge will cause only...
  9. Clara Chung

    I LS coupling and spin orbit interaction

    Why do you need a weak spin orbit interactions in individual electrons in order to use the LS coupling? From what I know, we are free to combined angular momentum whenever [L1, L2]=0 and this should be true on the orbital angular momentum (and spin) of the electrons because they are...
  10. Michaela SJ

    I A very small object following Earth in the same orbit

    A bunch of years ago, I read about a very small object following Earth in the same orbit, but not in any danger of collision with Earth (at least in the next few billion years). Anyone know about the object. I have done a search but cannot find any reference to what I think I read about?
  11. R

    How Does Satellite Mass Impact Velocity Change for Circular Orbit Achievement?

    Homework Statement Consider an elliptical orbit of a satellite (of mass m) around the Earth (of mass M >> m). The perigee is at ##r_A## and the apogee at ##r_B##, as measured from the centre of the Earth, itself located at one of the focal points of the ellipse (see Fig. 1). We work in an...
  12. P

    Perigee & Apogee: How Earth's Orbit Impacts Summer Temperatures

    does the Perigee and Apogee of the Earth's orbit relative to the seasons affect the temperature of our summers?
  13. T

    Why do we need the hyperbolic excess velocity?

    $$V_{HE}=\sqrt{\frac{\mu}{a}}$$ What is the rationale for this formula when we can determine the change in velocity from Earth's orbit to transfer orbit using the vis-viva equation? Likewise, what is the use of defining the radius for the sphere of influence for interplanetary transfer...
  14. AidenFlamel

    Writing: Input Wanted World destroying solar storm/binary orbit

    Soooo, hi PF, it's been a long time since I needed your help, but here I am again. I've been doing some worldbulding lately and I came up with this idea of a world in which civilisation and life are much, much older than in ours. Yet it isn't as developed due to some kind of natural disaster...
  15. cosmik debris

    I Frame Dragging Effect vs Spin Orbit Coupling in GR

    I believe that GR cannot describe exchange of classical intrinsic angular momentum and orbital angular momentum. The exchange of orbital and intrinsic angular momentum requires that the momentum tensor be non-symmetric during the exchange. GR cannot accommodate a non-symmetric momentum tensor...
  16. H

    I How would the DSG orbit the Moon?

    Assuming it happens and that the Deep Space Gateway happens as a base for Moon landing and further exploration. What sort of orbit would it have in relation to this use? I have I-searched but not found any detail. Thanks.
  17. T

    How much work is done when a satellite is launched into orbit?

    Homework Statement A Satellite is brought up into a geostationary orbit (altitude 35800km measured from the surface of the earth). Satellite weights 1000.0kg. How much work is required to bring satellite from a surface of the Earth to geostationary orbit? Homework Equations Newton's law of...
  18. F

    Writing: Input Wanted Duration: flights to L-4 point, and 90 degrees Earth orbit

    Assumptions: 200+ years from now Asteroids have been moved to all Lagrange points, and at least 90, 180, and 270 degrees on Earth's' orbit for mining, and shielding humans and equipment Tech to acceleration/decelerate at 1 gravity without need to carry fuel. (My main fiction.) Direct line of...
  19. C

    Double star mutual orbit calculations

    Homework Statement A tight pair of stars orbiting with circular paths at a distance a, the weight of the stars is the same: M1=M2=M What period T and frequency f is the pair circulating? Explain the results generally with G, M, a. Homework Equations Kepler's law M1+M2=a^3/T^2 The Attempt at a...
  20. M

    A Orbit velocity in Schwarzschild metric?

    Hi, I'm trying to deduce orbit velocity of a particle with mass from Schwarzschild metric. I know for Newtonian gravity it is: $$v^2=GM\left(\frac{2}{r}-\frac{1}{a}\right)$$ The so called vis-viva equation. Where ##a## is the length of the semi-major axis of the orbit. For Schwarzschild metric...
  21. X

    I Zero Gravity Near a Black Hole?

    This is probably a fairly simple question, but I am struggling with it. My question is: Would you experience the effects of gravity if orbiting in a stable or circular orbit close to a black hole? This stems from my mental image of the International Space Station (ISS). There is obviously...
  22. chasrob

    Is the Circular to Elliptical Orbit Calculator Accurate?

    I have an object in a 500,000 km circular orbit around earth. I want to change it into an elliptical orbit with a perigee of 500 km. I found this cool site and put those numbers in the calculator. The ”Injection into elliptical transfer orbit delta V” answer is -741.97 m/s. Does that mean to...
  23. H

    I Do trojan satellites follow migrating planets?

    Some or all of the planets are thought to have migrated long ago under the gravitational influence of Jupiter. Would the trojan matter at their L4 and L5 points have followed during their migration to new orbits? In other words, while the L4 and L5 points are approaching or receding from the...
  24. Edward Barrow

    I Would an exploded planet change earths orbit (see graphic)

    If a hypothetical planet was once where the asteroid belt is now, and was removed (for example exploded and fell inwards towards the sun where it got burnt up), would this cause the inner planets to migrate outwards into new orbits due to the orbital resonance lost by this hypothetical planet...
  25. Raphael30

    Hohmann transfer ellipse to Mars orbit from LEO

    Homework Statement We want to send a satellite from a low Earth orbit of 320 km to mars. Calculate the change in velocity required to join the transfer ellipse. Homework Equations Earth velocity: (μS/REarthRev)1/2 Transfer velocity at perihelion: (2μSRMarsRev/(REarthRev(REarthRev+RMarsRev))1/2...
  26. binbagsss

    Limit , circular orbit ,schwarzschild s-t ,

    Homework Statement [/B] To take the ##lim J \to \infty ##, what are the two roots of ##r_c## in this case... So I believe it says' ##J## big enough it had 2 solutions' is basically saying just avoiding the imaginary solutions i.e. ## J^4 \geq 12G^2M^2J^2 ## (equality for one route obvs)...
  27. L

    Planetary Motion: Orbit Transfers, Hohmann transfer

    The thought of increasing a satellite's (for example) speed to allow it to transfer from a "higher energy" elliptical orbit to a "lower energy" circular orbit (in reference to the effective potential energy plot that arises after introducing the concept of an effective mass to simplify the...
  28. Edge5

    I Does spin orbit coupling cause the split in the energy level of the electron?

    Hi, As far as I understand spin orbit coupling is the interaction between proton of atom and electron. Proton's motion(from the frame of electron) around electron creates magnetic field. Hence electron experiences magnetic field. Does this magnetic field produces a Zeeman effect which cause...
  29. N

    Orbital speed of an object in a circular orbit

    Homework Statement Consider a central force is attractive but which passes through the force center. In other words, consider an orbit of radius a which is centered at (a,0), with the force center at the origin c.) Suppose the speed at the apogee is v0 Find the oribital speed v as a function of...
  30. D

    I Time dilation for the Earth's orbit around the Sun

    If we have 2 atomic clocks on Earth's orbit around the Sun, one on Earth's surface, at one pole, and the other on a spaceship, far from Earth, but traveling with the same speed around the Sun, the clocks would suffer the same kinematic time dilation or not? I'm asking this because the clock on...
  31. shk

    Is the weight of a small satellite in its orbit zero?

    Is the weight of a small satellite in its orbit zero?
  32. N

    Elliptical orbit centered at the origin

    Homework Statement Under the influence of a central force F(r), a particle of mass m is observed to move in an elliptical orbit centered at the origin (the force center is not at one of the foci, as would be the case for a gravitational orbit) a.) Show that the polar equation has the form 1/r =...
  33. bbbl67

    What is the radius of the orbit of an electron?

    Homework Statement What is the radius of the orbit of an electron traveling at 9.0 x 10^6 m/s around a zinc nucleus which contains 30 protons? Homework Equations I don't know if this problem can be solved quantum mechanically, all I can think of doing is solving it classically, using Coulomb's...
  34. YMMMA

    Elliptical orbit/ determine speed & potential energy

    Homework Statement True statements about Jupiter as it moves in its elliptical orbit around the Sun include which o the following? I. It has its greatest speed when closest to the Sun. II. It has its greatest potential energy when farthest from the Sun. III. The magnitude of its...
  35. E

    B Can the moon orbit be used as perpetual motion?

    I'll attach a picture of what I mean but essentially I wanted to know if it was possible to (under circumstances where the Earth and moon do not change angle of rotation when orbiting the sun) create a perpetual motion machine using orbit as a means to turn a giant gear circling the Earth in...
  36. R

    B Earth's orbit around the sun -- looking for an equation

    Hi, I'm looking for some help please. I'm struggling to find an equation of the Earth orbiting around the sun. I don't need to include the mass of the sun and the gravity laws, etc. Just the equation to calculate a position in x and y. Can anybody help me please? My idea is to put the orbit...
  37. DLeuPel

    B Gravity - Do atoms orbit humans ?

    If the Earth orbits the Sun due to the difference in their mass and their distance, then do atoms like air particles orbit humans due to the same reasons?
  38. Bizmuth

    I Is a topopolis' orbit unstable?

    Background: Larry Niven's Ringworld was declared to be unstable because it rotates fast enough to create artificial gravity on the inner surface (never mind the structural material issues) and is therefore not technically in orbit around the central star. So I've been reading up on the...
  39. S

    Can I observe the atomic orbit with a universe sandbox2?

    Can't find a program at my level to simulate orbital or electron motor velocity, so is it possible to use universe sandbox2 to implement the atomic world to confirm the orbit? It is difficult to convert static electricity into gravity... It's hard to tell what the distance is between an electron...
  40. kenneththo85431

    Describing Electronic orbit in 3D space using A matrix.

    I've plotted out the trajectory of an imaginary electron in 3D; next I represent it's points with the matrix A(x1 y1 z1) "throughout it's orbit": ( -1/2 -1 1 ( -2 -1.5 2 (-1/2 2 3...
  41. H

    A Is there a topological insulator without Spin Orbit Coupling (SOC)?

    There are some famous materials is determined as TI induced by SOC, like graphene and so on. But from some formula, for instance, Kane-Fu formula, they just need parities to get Z2 number. So I wonder if there is a known TI with weak soc.
  42. L

    I Question about orbits and Kepler's problem

    I've been looking at the Kepler's problem, and it looks like your orbit (elliptic, parabolic or hyperbolic) are given in terms of energy and angular momentum. I was wondering: if I have a central attractive potential (such as the Sun) and a projectile starting from an infinite distance at a...
  43. caitphys

    Circular orbit change after gaining mass ejected from sun

    Homework Statement A satellite of mass m is in a circular orbit of radius R about a star of mass M. The star ejects 1% of its mass by means of a spherically symmetric wind which removes the mass to a large distance. What are the new nearest and furthest distances of the satellite’s orbit around...
  44. N

    I Satellite Orbit synchronization

    Consider a large non-rotating sphere, and one series of satellites, series A, in free fall orbit at the same velocity and altitude slightly above its "equator" going from east to west. Forming a ring in which all the satellites are equal distance apart, and another series of satellites, series...
  45. C

    A 3-star triangular orbit possible?

    Apparently 3-star systems aren't really 'doable' as in two stars, with one in-between- but nested binaries are possible. So is it 'possible' for 3 stars to maintain at least a somewhat stable triangular configuration?
  46. Timothy Schablin

    B What is the gravitational force like near a black hole?

    Found this interesting interactive experiment. http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q14.html In the interactive, it looks like the black hole is orbiting around something. What would it orbit around? Or am I looking at it wrong?
  47. M

    A Question for Distant Retrograde Orbit in CR3BP

    In the Sun-Earth system in circular restricted three body problem, how can i define the initial conditions for a distant retrograde orbit? The state vector has to be X=[x0 0 0 0 vy0 0]. How i define the initial position in x-direction and the initial velocity in y-direction.? What values do i...
  48. J

    B Lowest possible altitude for a Satellite

    What is the lowest altitude for a satellite to orbit?
  49. A

    Increasing the speed of a circular orbit

    What If the velocity of particle moving in a circular orbit has increased , would the particle be no longer in circular orbit or it would go in an orbit with bigger radius?
  50. E

    B Would planets fall out of orbit when gravity has a speed?

    As I understand it, Newton considered the influence of gravity between two objects to be instantaneous. Now it would appear that gravity has a speed limit. If the Earth is influenced by the sun from where it was 8 minutes ago, how does the Earth keep up with a traveling sun? Does relativity...
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