Orbit Definition and 1000 Threads

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. Biker

    Object in orbit vs. object falling through a planet

    If you haven't seen this video before then go watch it :D Question: Answer: It is pretty hard to imagine it as a spring and here is why: 1) At (o) the spring should move by its inertia not by any force. If we look at the planet we can summarize that there are 2 points (As I think) that could...
  2. L

    Range of Earth's year within habitable zone?

    Hi all, So the (hypothetical) question I have is about the range of the Earth's length of orbit (number of days) within the Sun's habitable zone which could sustain human life. I.e. what would the length of the shortest 'habitable' year be, and the longest (in days)? What would our living...
  3. R

    Time dilation magnitude in orbit around a black hole

    Hello, I'm working on a hypothetical situation involving a planetary body orbiting a black hole (similar to the scenario in Interstellar, but for different reasons), trying to balance tidal forces with orbital distance and time dilation. First, I'm interested in the effect of gravitational...
  4. J

    Electrostatic analysis of cad model of protons neutrons

    Could the orbit filling order of electrons be more classical and less quantum? I attached a jpeg and need someone to do a electrostatics analysis of the CAD model version of it. Does anyone have an electrostatics software package and have time to do a finite element analysis on a 3-D part to...
  5. Ontophobe

    Photon Orbit Around a Black Hole: Conservation Law Effects

    Hi. Now that I understand the conservation law of angular momentum, and given the fact that c is constant, I infer that if a photon were to go into orbit around a black hole, it could only take a circular orbit. No elliptical orbits for photons, because if it were to follow an elliptical orbit...
  6. M

    How to find the speed of a planet around the sun

    Homework Statement THe sun has a mass of 1.99x10*30 kg. Jupiter has a mass of 1.90x10*27 kg and a mean radius of orbit around the sun of 7.78x10*8 km what is the speed that Jupiter travels in its orbit around the sun? Homework Equations fg=(Gm1m2)/d*2 fc=(4pie*2mr)/T*2 The Attempt at a...
  7. T

    B Delta-v for orbit if already at ideal velocity and altitude?

    Lets assume you could fire a 100kg projectile using a coilgun at 1 degree above the horizon and have it arrive safely at 400km altitude traveling at 7.8km/s (or slightly more if that helps). How much delta-v would it need to correct its trajectory into a stable orbit? If it matters let's...
  8. 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...
  9. P

    Gravity Simulator 2D: Calculating Trajectories

    I want to create a simple 2d Gravity simulator where I have a large body i.e. A circle which could be a planet or the sun. I then want to simulate small comets or asteroids traveling past it, crashing into or being pulled into orbit. I know the gravitational force formula but that seems the...
  10. Jenab2

    A challenging transfer orbit question

    Assume that these orbital elements remain good for Vesta and for Ceres in the year 2080. Vesta. a = 2.3617272 AU e = 0.08889958 i = 7.14° Ω = 103.8467° ω = 151.1467° T = 2456923.543 Ceres. a = 2.7680973 AU e = 0.07575951 i = 10.5917° Ω = 80.3229° ω = 72.7187° T = 2456552.887...
  11. T

    Universal Gravitation problem - Satellite Orbit

    Homework Statement http://prntscr.com/9huihp Given, Mass of the Earth = 6*1024 Mass of Satellite = 45 kg Radius of Satellite's orbit = 4.2*107 G = 6.67*10-11 Find the velocity of the satellite. Homework Equations Gravitational Force Fg = (G*Me*Ms)/(Rs2) Newton's second law: Fg = Ms*a where a...
  12. mfb

    SpaceX SpaceX: First stage landed Satellites in orbit

    A great launch, everything worked as expected, delivering 11 OrbComm satellites to Earth orbit (they all got deployed in the minutes after reaching orbit). But that was the routine part... although it was the first flight of an improved version of Falcon 9 1.1 ("Full thrust" version). The first...
  13. C

    Correlation between orbit eccentricity and mechanical energy

    Homework Statement I have been tasked with showing "how the mechanical energy of a planet determines the shape of its orbit", and I cannot for the life of me make sense of it. I've run into a formula, see below, but I'm not sure how to interpret it nor if it even applies in my case at all (as E...
  14. james_dear

    Orbit of Cube Planet: Physics Explained

    What is the physics behind a orbit a cube planet. Does the convential physics including keplars laws and circular motion still apply. Also The cube having a centre of mass posited in the middle of the cude does this mean it can be consider point mass and the same as spherical planet orbit? any...
  15. lucphysics

    Kinetic and potential energy (satellite low orbit)

    Hello, I have this problem statement : "Due to air drag, the radius of a satellite’s circular orbit decreases from r to r - △r, where the positive quantity △r is much less than r. The mass of the satellite is m. Show that the increase in orbital speed is △v = +(△r/2)[(GM/r^3)^1/2]; that the...
  16. jcruise322

    Final velocity of satellite that falls from orbit

    Hey, how's it going! Just a little confused about how to do the problem below. Any help would be appreciated! 1. Homework Statement A satellite of mass m=100,000 kg is moving around the Earth in a circular orbit at an altitude of 100,000 feet above the surface. If the satellite were stopped and...
  17. G

    Ptolemy's Theory of the Empty Focus of an Elliptical Orbit

    An ellipse has two foci. For a planet in such an orbit, the star is at one of the foci. The other is empty. According to Ptolemy, if we draw a line connecting the planet and the empty focus, we will find that the line moves at a constant angular velocity. Is this true, or is it a crude...
  18. S

    Newton's Laws: Impact, Orbit & Weight

    1. Which will have the greater force during impact; a bumble bee being hit by a train or a train being hit by a bumble bee? (Hint: Newton’s Three Laws of Motion) 1. What is the centripetal force that holds the Earth in orbit around the sun? 1. How much does a 76.0 kg person weigh on Earth in...
  19. Y

    Two satellites A and B move around earth in a circular orbit

    Two satellites A and B move around Earth in a circular orbit. The mass of B is twice the mass of A then I agree that kinetic energy of B is greater than that of A. But what I couldn't understand was that why are speeds of A and B equal as given in the book. Shouldn't they differ according to the...
  20. Y

    Will Radial Escape Velocity Launch a Satellite Into Orbit?

    If we provide a satellite with escape velocity perpendicular to the earth(radially), would it start orbiting it?
  21. T

    Describing elliptic orbit as a parametric function

    Hi PF I've beent rying to model the lunar orbit around the sun (cardioide) as a parametric function, but have run into a problem. f(t) = r(t) : x = a cos(ωt) y = b sin(ωt) z = k t The angular frequency ω as well as the distance from to the center varies around the orbit. Is...
  22. D

    Time of satellite orbit around moon?

    Homework Statement What is the time of an orbit of a satellite around the moon close to the moon's surface? What quantities do you have to look up to be able to answer this question? Radius of moon is 1736482 meters Homework Equations F = Gm1m2/r^2 and maybe F=mv^2/r 2pir The Attempt at a...
  23. A

    Watching Earth travel in space....what should be the location

    Dear All, Is it possible to watch Earth orbiting the sun in space like we watch a car coming towards us on a highway ? I mean, I would like to see it coming towards my spaceship at the rate of say 50 km/hr. Now some questions - 1. What should be my location and speed of my spacecraft...
  24. ScramjetCCO

    Continuous thrust orbit changes

    Most threads about making orbit changes assume impulsive changes in velocity (short period bursts). What if one wants to increase the radius of a circular orbit with a very small constant thrust? I assume the thrust should be applied tangentially in the direction of travel, but what would be the...
  25. J

    What Is the Most Relevant Contribution to Earth's Orbit After the Sun?

    If one writes down the Newton's equations of motion for the Earth, the forces that act on the Earth are the gravitational forces exerted by all other massive bodies, such as the Sun, the Moon, the planets etc. The largest of these forces is that of the Sun: keeping into account only the Sun's...
  26. I

    Earth's orbit & precession affected by Venus & Jupiter?

    I watched a program that said that some of Earth's past climate change was due to variations in Earth's orbit and precession due to the the gravitational perturbations caused by Venus and Jupiter. Why would that be so? I know that the orbits of the planets are eliiptical generally and they...
  27. Buzz Bloom

    Why low precision of the radius of Sun's orbit in MW?

    It seems that the value has only 1 1/2 significant digits. Why are values for the measurement of this radius not more precise? What prevents a greater precision? I have recently been trying to learn about the sun's orbit in the Milky Way (MW) in order to calculate estimates re DM for another...
  28. Z

    How Is Energy Transformed in a Satellite's Decaying Orbit Due to Air Friction?

    Homework Statement A 500-kg satellite is in a circular orbit at an altitude of 500 km above the Earth’s surface. Because of air friction, the satellite eventually falls to the Earth’s surface, where it hits the ground with a speed of 2.00 km/s. How much energy was transformed into internal...
  29. 0

    Non-Central Forces in N-body Problems?

    For a 2-body system that is not under the influence of an external force, the forces on each body (assumed to be point particles) always point to the center of mass the 2-body system. Does this still hold for general N-body problems, where N>2? Specifically, does the net force on each body...
  30. F

    Understanding Spin-Orbit Coupling in Quantum Mechanics

    So we obtain the perturbation Hamiltonian H as something proportional to S.L/r3 and the first order energy shift is then the expectation value of this perturbation Hamiltonian in the state that is being perturbed. So let a general gross structure state that we are perturbing be |n l ml s ms >...
  31. P

    Solve Orbital Mechanics Problems: Calculate Satellite Energy

    I'm having trouble with orbItal mechanics, I'm trying to determine the total potential energy of an orbiting satellite, what I've done so far is this: I know m*g*h is potential energy, but I also know that gravity deceases with distance avoiding to the inverse square law. I know I Just can't use...
  32. H

    How do we orbit the sun when you can set your origin anywhere....

    As I understand it a coordinate origin is just chosen for convenience. So how can we state the Earth revolves around the sun when you could make coordinate origin at any point in the universe??
  33. I

    Satellite Position: Calculating ECI from ECEF

    Homework Statement Hi! I just found this forum after trying to calculate something regarding a satellite's orbit. Hope that you can help me here. So, I need to calculate the matrix of a satellite's site vectors. I have found it in the ECEF form, but since the satellite is doing observations in...
  34. xpell

    Heliocentric polar orbit crossing the Earth's orbit twice

    Sorry, the title's length didn't allow me to explain this better and I need it for a story that I'm writing, if you're so kind to help me. I've been trying it hard to solve it myself but I've been unable to. The problem looks simple but it isn't (for me): Please assume we have a space probe of...
  35. Buzz Bloom

    Orbit Dynamics in an Expanding Universe

    After learning a bit from the thread "The Dark Sky Ahead", I have tried to think through the dynamics of gravitational interactions in a simplified scenario. Unfortunately the GR math of the problem is over my head. My attempt below, using a simpler approach, leaves me quite confused. If my...
  36. T

    Why does Mercury have an elliptical orbit?

    Why is mercury obit elliptical? Is it because of the curvature of spacetime caused by the presence of sun such that the mercury moves in that orbit otherwise known as geodesics? However what about the other planets like Earth that orbits in a circular orbit? Is is just that that is their...
  37. edguy99

    Model Mercury Orbit w/Relativity: Force of Gravity Calc Explained

    This question relates to building a computer model of gravity under relativity in a frame by frame type animation where the force on an orbiting object is calculated between each frame and applied to the animation. Its pretty easy to model normal planet orbits using Newtons inverse square law...
  38. Cibo Matto

    Orbit decay of particles w/ synchrotron radiation?

    Hello everyone! I had a question about a particle (say a proton) with relativistic energies interacts with a magnetic field (in the z direction). As it is accelerates the particle emits synchrotron radiation. Naturally I assume that this emission of photons reduces the particle's energy. My...
  39. Keermalec

    Time dilation in an elliptical orbit

    The formula for time dilation in a circular orbit is readily available but the literature seems to indicate it would not be so simple in the case of an elliptical orbit, and no simple formula seems to be available. Given that time dilation in a circular orbit adds the velocity effect (GM/r) to...
  40. T

    Connection coefficients in Earth orbit

    I've run into a couple of problems with exercise 12.6 in MTW (attached). At this stage, all I'm asking is for someone to give me answers to the following questions: 1. What are the Rα'β'γ'δ' in the primed co-ordinate system? and 2. What are the non-zero connection coefficients in the...
  41. I

    Elliptical Orbit of Sun Around Milky Way

    Hi, I'm new to this forums (and please forgive my grammer and sentence structure as my first language is not English and I'm trying my best :) I'm just a teenager who has great interest in these types of stuff, never did any proper education relating to this, just some research out of curiosity...
  42. vinicius0197

    Change in mechanical energy (gravitation)

    I got a little bit confused while studying gravitational potential energy, particularly the expression for long distances: (-GMm/r). An exercise asks me for the velocity, period and radial acceleration for a 1000kg satellite that I wish to put into orbit. That's okay. But after that, I'm...
  43. S

    Confusion About the Physics of Orbiting Bodies

    I hope this is in the right thread, I wasn't sure which one to put this in but this seemed like the most likely one to be right, so I'm sorry if this is in the wrong thread. Anyway, my question basically amounts to this: what is the difference between something orbiting around a still planet...
  44. saadhusayn

    Finding out the type of central force given the orbit

    Hi, This is the statement of the problem of AP French's textbook "Newtonian Mechanics". 1. Homework Statement The commander of a spaceship that has shut down its engines and is coasting near a strange-appearing gas cloud notes that the ship is following a circular path that will lead...
  45. H Smith 94

    Can Light Orbit a Massive Object?

    According to Hawking [1] it is posited that light photons at the event horizon of a black hole must cease to move, and remain motionless for the entire lifetime of the black hole. It is also observed [http://dls.physics.ucdavis.edu/~scranton/LensedCMB/a2218.gif] (and calculated) that the path...
  46. C

    Moving an asteroid into earth orbit

    Hi, I'm trying to figure out how big an asteroid we might be able to "capture" and bring back into Earth orbit for mining - both with today's technology and with potential technologies of the future. Specifically I am looking at a rock that is 500 feet in diameter and relatively round. My math...
  47. GiantSheeps

    Why isn't the Oort Cloud shaped like a disk?

    Why isn't the Oort Cloud shaped like a disk like the asteroid belts and how the planets orbit? Also, why exactly do the planets orbit in that flat disk shape?
  48. T

    How Do You Calculate the Semi-Major Axis of a New Elliptical Orbit?

    Homework Statement (a) A satellite is initially in a geostationary orbit around the Earth, so that the satellite always remains above the same point on the Earth’s equator. Show that the radius of the orbit is ##4.22\times 10^7##(b)An engine is briefly fired in the direction of the satellite’s...
  49. mgkii

    Neil deGrass Tyson "Orbital Erosion"

    I listened to one of NDT's lectures on a podcast this morning and he made a passing reference to two black holes orbiting each other that would eventually "spiral into each other due to orbital erosion" (his words) I'm familiar with orbital decay for satellites in orbit around the Earth due to...
  50. Monsterboy

    A single stage vehicle all the way to orbit

    http://m.space.com/19872-skylon-space-plane-human-spaceflight.html I don't have a background in aerospace engineering but I am interested to know the main reasons as to why it is so difficult for single stage vehicle to go all the way to orbit. Is it about the fuel constraints and the weight...
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