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. P

    Achieving an 895 km Orbit: Calculating v

    How fast must a satellite leave Earth's surface to reach an orbit with an altitude of 895 km? Ek + Eg (earth) = 1/2 Eg (could you please show how to substitute to solve for v) this question is on the forum and it was suggested to add this v once calculated to 7404.5 m/s which was calculated...
  2. V

    Elliptical Orbit Question with no numbers

    Homework Statement A satellite of mass m is in an elliptical orbit around the Earth, which has mass M and radius R. The orbit varies from closest approach of 'a' at point A to maximum distance of 'b' from the center of Earth at point B. At point a the speed of the satellite is vo. Assume Ug...
  3. P

    What is the new orbit if k is halved in a circular orbit with F(r)=-k/r^2?

    Homework Statement A particle in circular orbit moves in a force field given by F(r)=-k/r^2. If k is halved what will the new orbit be? Homework Equations The answer is the orbit becomes parabolic but how? how does the total energy become zero as for parabolic orbits total energy=0...
  4. Math Jeans

    Oscillation of disturbed constrained circular orbit

    Homework Statement Consider a particle of mass m constrained to move on the surface of a paraboloid whose equation (in cylindrical coordinates) is r^2=4az. If the particle is subject to a gravitational force, show that the frequency of small oscillations about a circular orbit with radius...
  5. A

    Space shuttle Atlantis orbit question

    Homework Statement True or False: The space shuttle Atlantis follows an essentially circular obrit for most of it's operational time on a mission. While in orbit, the gravity of the Earth does not do any work on the shuttle because the shuttle is not accelerating. Homework Equations...
  6. A

    Moon's Orbit: Moving Closer or Farther From Earth?

    It was reported that the Dec 12th moon was the closest it has been to Earth in 15 years. I've always heard that the moon is actually moving away from the Earth. Is the moon in a specific orbit? Or does its orbit change and if so, does it change in a specific way?
  7. S

    Runge Kutta Algorithm Solve Differential Equations for Satellite Travel from Earth to Jupiter?

    Hi, i am trying to solve the following differential equations for a satellite traveling from Earth to Jupiter using a runge kutta algorithm. The equations are: dr/dt=+-(h/r)[((r/r0)-1)(1-(r/r1))]^(0.5) and dr/d(theta)=+-r[((r/r0)-1)(1-(r/r1))]^(0.5). where r0 and r1 are the radii...
  8. C

    Creating a 3D Planet Orbit Simulator

    I am making a three dimensional planetary orbit simulator but I can't figure out a formula that can work out where a certain planet is at a certain time e.g. if a planet with speed s was at position a with the sun at position b at time 0 then how would I calculate the position of the planet at...
  9. P

    The most distant object that can still orbit the Earth.

    Hi all, I am puzzled as to how far an object can still be influenced by the Earth gravity. The same question with the Sun as the central object. Thank you.
  10. G

    What is the period of orbit for a space station placed 30 000km from the Earth?

    Homework Statement A space station is placed in an orbit of radius 30 000km. What is the period of the station's orbit around the Earth? (I previously worked out the period of rotation of the space station as 22 secs but I didn't think it was relevant to this part of the question besides...
  11. G

    Calculating the Period of an Orbit around Earth

    Homework Statement A space station is placed in an orbit of radius 30 000km. What is the period of the station's orbit around the Earth? (I previously worked out the period of rotation of the space station as 22 secs but I didn't think it was relevant to this part of the question besides...
  12. R

    Functions that define an orbit

    In a simple flat 2 dimensional plane of a two body orbit, both circular & elliptic. How do you write the functions wrt “t” time for: 1) Force vector equation (that applies acceleration) 2) Velocity vector equation 3) Position vector equation That allows applying simple calculus...
  13. D

    Can Satellites Measure Earth's Geode Using Velocity Instead of Position?

    Hello, layman question here. Suppose a spaceship approaches a highly massive body, at great speed; it violently swings around the body and comes back in less than a minute. All in a free trajectory, with thrusters never applied. The question is: would the occupants of the ship be crushed...
  14. T

    Circular motion (planetary orbit) question

    Homework Statement A turntable is spinning at 100 rpms. It has a mass of 2kg and a radius of 0.1 meters. 2 blocks of mass 0.5kg fall simultaneously on 2 opposite ends of a diagonal and manage to stick. What is the new angular velocity of the turntable after the blocks stick? Homework...
  15. snoopies622

    Verifying Lagrange Equations for Orbit around Massive Body

    I am trying out the Lagrange equations for the first time, in this case for a particle in orbit around a massive body using classical mechanics. I come up with 2 \dot r \dot \theta + r \ddot \theta = 0 \ddot r - r \dot \theta ^2 + \frac {GM}{r^2}=0 These seem credible to me...
  16. S

    Putting an item into orbit. Help

    Homework Statement No idea how to do this honestly, but here it is. Hopefully someone can just work this out and I can learn from that. Calculate the velocity needed to place a 14.5kg item (its a turkey but whatever lol) into orbit around the Earth at an elevation of 100km. The radius of the...
  17. Philosophaie

    Elliptical orbit around the Sun

    Why do the planets travel in elliptical orbit around the Sun?
  18. C

    How Do You Find A Central Force Orbit?

    If you are given a central force field and an initial velocity of a particle in this field, how would you go about finding the orbit of the particle in polar coordinates? Thanks for you help and time.
  19. D

    Meteor Entering Orbit of a Sun (cons. energy & momentum) [very hard algebra]

    Homework Statement Alright, so I've given this guy a few cracks, and I think I'm close to it, but apparently I'm not right, so here's how it goes. Simple in concept. A meteor moves toward the solar system with speed v0 in a direction such that it would miss the sun by a distance d if it...
  20. C

    Calculating Work for Satellite Orbits Around Earth

    Homework Statement A satellite mass 481 is in circular orbit of 9.29x10^6 m above the surface of the Earth the weight of a 65.1 kg astronaut inside the satellite What work was done (ignoring friction) to put the satellite into this orbit. Assume it started at rest on the surface of the Earth...
  21. C

    How Much Energy Is Required to Launch a Satellite into Orbit?

    1. Homework Statement A satellite of mass 200 kg is launched from a site on Earth's equator into an orbit at 205 km above the surface of Earth. What is the minimum energy necessary to place the satellite in orbit, assuming no air friction? I also figured the orbital period to be 5300 s and...
  22. M

    The period of earth's orbit

    Please help... Given that the distance to the sun from the Earth is 1.5*10^11 m and the the mass of the sun is 1.9*10^30 kg. Using Keplers law find the period of the Earth's orbit recorded in seconds; show how to express your anwser in years; and if your anwser does not agree with the accepted...
  23. MTd2

    Pioneer anomaly possibly found manifest in Saturn orbit.

    Now it’s Saturn’s turn to flummox astrophysicists. The Russian astronomer Elean Pitjeva, who heads the Laboratory of Ephemeris Astronomy at the Institute of Applied Astronomy in St Petersburg, has analysed a huge data set of planetary observations dating back to 1913, including 3D observations...
  24. S

    Angular speed of earth in its orbit

    Homework Statement Express each of the following in radians per second: (a) 720 ; (b) 50 ; (c) 1000 ; (d) 1 (which is the angular speed of Earth in its orbit). Homework Equations why all my answers are wrong? please help me! The Attempt at a Solution
  25. V

    Escape velocity FROM a satellite in orbit?

    The question: At what speed would a small object have to be launched from the satellite in order to escape earth’s gravity, assuming that the satellite is not moving? The satellite is in circular orbit around the Earth and the radius of the orbit is 4.22 x 10^7. The main problem I am having...
  26. D

    Calculating Angle and Frequency of Mars-Sun Opposition

    Mars orbits the sun at a mean orbital radius of 228e9 m and has an orbital period of 687 d. Earth orbits teh sun at a mean orbital radius of 149.6e9 m. a)The earth-sun line sweeps out an angle of 360 degrees during one earth-year. Approximately what angle is swept out by the Mars-sun line...
  27. L

    Circular kinematics a star in orbit around another star.

    i got part a, but i can't get part b! 1. A star has a mass of 2.96 x 10^30 kg and is moving in a circular orbit about the center of its galaxy. The radius of the orbit is 3.3 x 10^4 light-years (1 light-year = 9.5 x 10^15 m), and the angular speed of the star is 1.6 x 10-15 rad/s. (a) Determine...
  28. P

    Derive Angular Momentum in Elliptical Orbit

    Homework Statement A planet with mass m is orbiting about the Sun (mass m(s)) with elliptical orbit such that the maximum and minimum distance is r1 and r2 respectively. What is its angular momentum, L, of the planet relative to the centre of the Sun? Homework Equations...
  29. P

    Derive angular momentum of planet with elliptical orbit

    Homework Statement A planet of mass m orbiting the Sun(mass=m_s along an elliptical orbit, with aphelion r1 and perihelion r2. Find the angular momentum of the planet relative to the centre of the Sun. Homework Equations Angular momentum, M=m(R\times v)=mvR sin\theta Distance from Sun...
  30. M

    Orbit Collision: Find New Earth Orbit Axes (A,B) in Terms of R

    Homework Statement If Halley's comet hits the Earth head on and after the collision the Earth continues to move in its initial direction but with 12% greater speed, find the new semi-major and semi-minor axes on the new Earth orbit in terms of the earth-sun distance (R) for the present...
  31. fluidistic

    Question about sending satellite circular orbit

    Is it possible to put in circular orbit an object from Earth's ground? My friend said yes and told me we were going to see how exactly in 2 years when we'll learn about a more formal mechanics. But I've thought about it and I believe it's impossible. My thought is that the satellite will...
  32. M

    Solving Elliptical Orbit Homework: Comet's Semi-Major Axis & Sun Distance

    Homework Statement The period of a comet orbit is 100 years. As its closests approach is 0.37 AU from the sun. What is the semi-major axis of the comet's orbit? How far does it get from the sun? Homework Equations (T1/T2)^2 = (s1/s2)^3 The Attempt at a Solution I don't even know...
  33. S

    Why Does My Satellite Orbit Calculation Not Match the Expected 1.8 Hour Period?

    At what altitude will a satellite complete a circular orbit of the Earth in 1.8 hours? i used r=(GMT^2/4pi^2)^1/3 -Radius of the earth. but I am keep getting wrong answer please help
  34. A

    Solving Orbital Motion using ODE45 - MY Problem

    MY problom is easy,but i can't get the reasonable answer.problom dipicted: In the Cartesian coordinates,A satellite'higth is 200KM,and just in two dimensions.the initial position is （-6571KM，0），and initial velocity is （0，-7.8KM/S）.I need the final running solution of program.I want to solve the...
  35. E

    Satellite. calculate radius of orbit

    Homework Statement satellite is in a circular orbit around the earth. The period of the satellite is 25.4 hr. Calculate the radius of the orbit of the satellite. Data: Mass of the Earth = 5.98 x 1024 kg
  36. Philosophaie

    Earth's Orbit & Tilt in N. America: Winter Closest, Summer Farthest

    In the Northern Hemisphere of North America is the sun closest in the elliptical motion in the winter but the tilt is away from its intensity at the Tropic Of Capricorn? In the summer is the sun farthest in the elliptical motion but the tilt is toward the Tropic of Cancer and North America?
  37. A

    Gravitation - Satellite in circular orbit

    Homework Statement A satellite of mass m, initially at rest on the earth, is launched into a circular orbit at a height equal to radius of the earth. What is the the minimum energy required for this purpose? Homework Equations GMm/r^2 = mv^2/r PE at surface = -GMm/R PE at orbit =...
  38. Philosophaie

    Calculating the Earth's Elliptical Orbit around the Sun

    To help me you will need tho know Excel VBA very well. Earth has an elliptical orbit around the sun. JPL's website has the data to calculate this orbit: http://ssd.jpl.nasa.gov/txt/p_elem_t1.txt In the spreadsheet the parameters are calculated from widely used equations and some of my...
  39. L

    Which electron configuration is not possible for As? Don't know much about spdf orbit

    11. Which one of the following sets of quantum numbers (n, l, ml, ms) could not possibly describe one electron of an arsenic atom (Z = 33) in its ground state? (A) 2, 1, -1, 1/2 (B) 4, 2, 2, -1/2 (C) 3, 0, 0, -1/2 (D) 3, 2, -2, 1/2 (E) 4, 1, 0, 1/2 Solution: Electron configuration...
  40. N

    N-Body - Moon won't stay in orbit

    A long time ago, I wrote a program that takes bunches of particles and applies Newtonian gravity to each so they interact. Lately I've rewritten this program, in an effort to simulate planetary motion. However I've ran into a bit of a snag, I can get a Sun-Earth system to behave properly, and I...
  41. S

    SpaceX SpaceX's Falcon1 Rocket Achieves Orbit

    SpaceX's Falcon1 Rocket Achieves Orbit! Here's an article on Wired.com with an embedded Youtube video! http://blog.wired.com/wiredscience/2008/09/space-x-did-it.html Woohoo! Let the private space age begin! :cool:
  42. G

    Calculating Geosynchronous Orbit for a Satellite Around Jupiter's Moon

    Homework Statement 1. One of Jupiter's moons has a mass of 4.80E+23 kg and a radius of 3000.0 km. How high above the surface of the moon should a satellite of mass 183.0 kg be so that it undergoes geosynchronous orbit about the moon? The rotational period of the moon is 0.2639 days. 2...
  43. S

    Astrophysics- Calculate the altitude of a geosynchronous orbit

    a)Calculate the altitude of a geosynchronous orbit (an orbit that has an orbital period of one sidereal day)(altitude is measured from the surface of the earth/ The "r" in gravitational equations is always measured from the center of mass of an object. one may assume a circular orbit.) b) how...
  44. B

    Astronomy: Calculating Neptune's Mass from Triton's Orbit

    This question has been stumping me on my Astronomy homework for the past couple of days. I've tried to input the question into any of the other formulae that we've studied, but I keep drawing a blank on it. Homework Statement Given the size of Triton's orbit(a = 355,000,000 meters) and...
  45. L

    Calculating Tension in a Massless Cable for a Moon Orbit

    Homework Statement Suppose the moon were held in its orbit not by gravity but by the tension in a massless cable. You are given that the period of the moon's orbit is T = 27.3 days, the mean distance from the Earth to the moon is R = 3.85 x 10^8 m, and the mass of the moon is M = 7.35 x 10^22...
  46. K

    Elliptic orbit from empty focus

    hello, I am solving a problem about the angular velocity in an elliptic keppler orbit as seen from the empty focus of the ellipse. Homework Statement Show that the angular motion of a keppler orbit as seen from the empty focus is uniform to first order in the eccentricit. The Attempt at a...
  47. N

    How much work is done by the thrusters on a shuttle changing distances of orbit

    Homework Statement a 2000kg lunar lander is in orbit 40km above the surface of the moon. it needs to move out to a 500km orbit in oder to link up with a mothership that will take the astronauts home. it wants the answer in joules Homework Equations ??E2-E1=Work done by non conservative...
  48. T

    Orbital question(elliptical vs circular orbit)

    are there two points or one in an elliptical orbit where the speed is equal to the speed of a circular orbit at the same radius? if so what is the expression for this point? Thank you
  49. B

    Basic question about sun's mass & orbit of planets

    This came up on another website I read, and it got me to wondering, so I am certain someone here could answer this. The sun is constantly losing mass, as it converts its mass to energy. As it loses mass, its gravitational field weakens, because the gravitational field of a body is directly...
  50. Q

    Isometry and orbit dimensions

    Hi people, I just need to verify that I understand this correctly. For some four dimensional manifold and group of isometries: the dimension of the isometry group is given by the number of Killing vectors, while the dimension of the orbit group is given by the number of linearly...
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