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. M

    Gravitation and its effect on elliptical orbits

    Homework Statement Comets travel around the sun in elliptical orbits with large eccentricities. Suppose the comet has an initial speed of 1.17*10^4 m/s when at a distance of 4.9*10^11 m from the center of the sun, what is its speed when at a distance of 5.9*10^10 m? Give your in m/s in...
  2. D

    Why Doesn't Earth Fall into the Sun Due to Gravity?

    Why doesn't the force of the sun's gravity, cause a drag on the Earth and cause it to slow down and fall into the sun? For, example, if I have a North Pole magnet, and project(throw) a South Pole magnet around it, no matter what speed and direction of my initial throw, will not cause the...
  3. D

    Keplerian Orbits: Does a=v^2/r Still Apply?

    In a Keplerian orbit (an ellipse), the acceleration vector always points to the focus containing the central mass. Since that means the acceleration vector is no longer orthogonal to the orbit (except at two points), does the relation a = \frac{v^2}{r} still apply if we consider v to be the...
  4. Y

    Why are the orbits elliptical in shape?

    I have been told most of the planets around the sun have orbots elliptical in shape. I now understand that the orbits are formed due to 2 forces. i.e gravity of the parent body acting against the velocity of the orbitting body. The above only tells me that all orbitting objects should...
  5. S

    Plotting Elliptical Orbits: A Guide for Beginners

    How would you plot the orbits of planets? I know how to calculate velocity and all the other aspects of an obit but I don’t know how to plot elliptical orbits. (This is not homework)
  6. D

    Can You Determine the Center of Mass Distance Using Instantaneous Orbital Data?

    I've been doing some calculations but am obviously too dumb to work out something which should be straightforward (and no, this isn't homework) In a circular orbit, the acceleration is related to the tangential velocity and the radius via a=v^2/r In an elliptical orbit, both the velocity and...
  7. C

    How to Calculate Satellite Launch Speed for an Elliptical Orbit?

    Homework Statement It is required to put a satellite into an orbit with apogee of 5R/2, where R is the radius of the planet. The satellite is to be launched from the surface with a speed vo at 300 to the local vertical. If M is the mass of the planet show that v0=5GM/R (use conservation of...
  8. S

    What Are Orbital Vectors and How Do I Calculate Them?

    I'm fairly new to astrophysics, but I'm genuienly interested on knowing how to calculate orbits. I've been trying to do so on my own but I just find myself extremely frustrated. :confused: I'm trying to figure out what orbital vectors are and how i can calculate them using known orbital...
  9. T

    Hohman orbits University Physics I

    Homework Statement Im not sure how to solve this one... Hohmann orbits are the lowest energy orbits to move things from one planet to another in a solar system. In order to send something from the Earth to another planet in the solar system, you launch the object when the Earth and...
  10. L

    Hohmann transfer orbits (delta-v)

    I am writing an essay on Space travel for my A level coursework. I am writing about Hohmann transfer orbits. At the moment I am using the wikipedia page: http://en.wikipedia.org/wiki/Hohmann_transfer_orbit It explains how you can derive this: From this: I can't do the in...
  11. L

    Satellites, Orbits and Gravitational Energy

    Two satellites, A and B, both of mass m = 110 kg, move in the same circular orbit of radius r = 7.45 x 10^6 m around Earth but in opposite senses of rotation and therefore on a collision course. (a) What is the total mechanical energy EA + EB of the two satellites + Earth system before the...
  12. M

    How does a sudden doubling of the mass of a star affect the orbit of a planet?

    Suppose you have a star of mass M and a planet of mass m orbiting around it. The orbit is circular. m<<<M. U of course is -GmM/r^2. E of course is going to be -U/2 and kinetic energy U/2 due to the virial theorem. What would happen if the mass of the star suddenly doubles? This is...
  13. K

    Orbits of Transitive Group Actions

    Homework Statement Suppose G is a finite group, which acts transitively on a set X and let H be a normal subgroup of G. Show that the size of the orbits of the action of H on X are of the same size. Homework Equations The Attempt at a Solution I haven't been able to get very far...
  14. W

    Stellar orbits around the milky way.

    I was just thinking about how this is done. I have looked online and I can't find a none mathematical explanation. If I am getting it right, we get the orbits by measuring the radial and tangential velocities of several stars relative to our sun. I thought the tangential velocity was...
  15. O

    Why are planetary orbits so circular?

    Over in another forum I've got myself in trouble by suggesting that theoreticians haven't paid enough attention to this question. George Jones has kindlyhttps://www.physicsforums.com/showthread.php?p=2100856#post2100856" that the question seems to have been answered along the lines of...
  16. S

    De broglie wavelength and orbits

    Homework Statement If the be Broglie wavelength associated to the first orbit of the electron inside the atom of hydrogen is 62.4 nm, what is the wavelength associated to the fourth orbit? 1. 62.4 nm 2. 124.8 nm 3. 312 nm 4. 249.6 nm Homework Equations # of...
  17. W

    What is the Orbital Speed of a Satellite in a Circular Orbit?

    Homework Statement #1 A satellite is in a circular orbit around an unknown planet/ The satellite has a speed of 1.70 x 104 m/s, and the radius of the orbit is 5.25 x 106 m. A second satellite also has a circular orbit around this same planet. The orbit of this second satellite has a radius...
  18. K

    Fortran Calculating Orbits: Finding Satellite Distance from Earth

    I am doing a problem with calculating orbits. The orbit can be expressed in polar coordinates as r=p/(1-ecos(theta)) where r and theta are the distance and angle of the satellite from the center of the earth, p is a paremter where p=1200 km, and e is a parameter representing eccentricity. I'm...
  19. K

    Why Do Orbits Take an Elliptical Shape?

    why are the orbits elliptical in shape?i know that force equations give differential equations whose solutions imply that the orbits elliptical in shape.but what is the particular physical reason behind it?
  20. L

    Question about electrons, energy levels and orbits

    To make my question clear, i'll talk about the hydrogen atom. The energy of the electron level is -13.6 eV / n^2. This means that the higher the orbit (n), the higher the energy. Still, I've always read that K-shell (n=1) electrons are strongest bound. Yet when an electron goes from a high...
  21. A

    Exploring the Mystery of Coplanar Orbits

    Our solar system is often depicted, as it is on the poster on my wall, as the Sun and all of its satellites in coplanar orbits around it. I thought, however, that this "flat" representation was just a creative liberty taken to make is possible to put on a poster, but now I come to find out that...
  22. A

    Kepler's Law and Non-terrestrial Orbits (Not Earth)

    Homework Statement A satellite orbits a planet at a distance of 6.80 multiplied by 10^8 m. Assume that this distance is between the centers of the planet and the satellite and that the mass of the planet is 3.08 multiplied by 10^24 kg. Find the period for the moon's motion around the earth...
  23. I

    "Calculating Work Needed to Change Orbits

    Homework Statement A shuttle orbiting the Earth at 400km deploys a satellite of mass 800kg into orbit a further 200km from earth. Calculate the work that must be done by the shuttle to deploy the sattelite. Homework Equations E_{k} = \frac{GMm}{2r}, U = -\frac{GMm}{r} The Attempt at...
  24. H

    How Much Delta-V is Needed for a Hohmann Transfer to Mars?

    Homework Statement Estimate the total delta-V required to perform a Hohmann transfer between the Earth and Mars, ignoring the gravitational influences of the two planets. The planetary orbits may be assumed to be circular and in the same plane. Why will there be a minimum wait time at...
  25. M

    Mechanics - Orbits under Central Force

    Homework Statement A particle moving in a plane is attracted towards a point (fixed) by a force zr^-5. The particle is projected from an apse at distance a with speed SQRT(z/(2a^4)). Show that the orbit is r=acos(theta) Using the Orbit Eq: d^2 u/dC^2 + u = za^-5/(hu)^2 h = angular...
  26. C

    Work done in elliptical orbits

    Homework Statement http://img47.imageshack.us/img47/7206/wtffffftv0.th.jpg http://g.imageshack.us/thpix.php Homework Equations Work is the dot product of force vector and displacement vector. Centripetal acceleration is velocity squared divided by radius -- multiply by mass to get force...
  27. thenewmans

    Quantization of Color: Electrons Jump Between Orbits

    Is there any paper on the quantization of color? Maybe not since it’s obvious. I always thought that color was on a continuum. But now I realize that electrons jump between a limited set of orbits.
  28. F

    Electron 'Orbits' and the Uncertainty Principle

    I was reading the faq and it said this quote: It turns out that the picture of electrons moving in circular orbits around the nucleus isn’t correct either(*). The solution here is the implementation of Quantum Mechanics via the Schrödinger Equation and the concept of wavefunction. By...
  29. J

    What is the Period of the Hubble Space Telescope's Orbit?

    Homework Statement The Hubble Space Telescope orbits Earth 614 km above Earth's surface. What is the period of the telescope's orbit? Homework Equations T=(2*pi*radius)/v The Attempt at a Solution No attempt, Using that equation, I'd have to know the velocity, and that is where...
  30. N

    Electric Potential Energy of electron orbits

    An electron and a proton are initially very far apart (effectively an infinite distance apart). They are then brought together to form a hydrogen atom, in which the electron orbits the proton at an average distance of 5.43 * 10-11 m. What is EPEfinal - EPEinitial, which is the change in the...
  31. A

    Heisenberg Uncertainty Principal with regards to electron orbits

    Hello all, I have gathered that the orbit of an electron cannot be calculated due to the uncertainty principal which states that position becomes uncertain when momentum is measured and vice versa. From this I understand that an orbit is not possible for an electron, hence the term...
  32. M

    Orbits &amp; Projectiles: Why the Difference?

    Hello everyone, Why is it that in projectiles we learn that a mass launched horizontally will always fall towards gravity regardless of its horizontal velocity but in orbiting satellites this does not happen? Thanks!
  33. V

    Rotational Motion and Gravity/Planetary Orbits review

    I have a test Monday and I'm trying some review problems my professor gave us to study from. I'm not looking for answers I'm just looking for someone to help step me through a few of these problems. Thanks for any and all help you guys can provide. Homework Statement 3a). After starting...
  34. L

    Solving Planetary Motion: X & Y's Circular Orbits

    Homework Statement Planets X & Y travel in circular orbits around the same star. The ratio of the radii of their orbits is 5:2. 5 years after the planets were aligned, planet x has rotated 92.6 degrees. how many degrees has y traveled in the same amount of time? Homework Equations...
  35. J

    Q on satellite orbits + orbital drift

    Im aware that due to the oblate nature of the Earth, the satellite's line of apside and line of nodes rotate according to the following formulas (where i = angle of inclination of orbit to Earth and K is mean motion per day) Variance in right ascension of ascending node (\Omega) due to...
  36. J

    Q on Satellite Orbits + Regression of Nodes

    Currently I am studying about mechanics of satellite orbits, however I cannot seem to understand in the regression of nodes, why the line of nodes would rotate in a direction contrary to that of the actual satellite orbit (irrespective if it is prograde or retrograde orbit) ? Ive tried...
  37. N

    Circular Orbits of Satelites and Planets

    Homework Statement A spy satellite is in circular orbit around Earth. It makes one revolution in 6.00 h. A. How high above Earth's surface is the satellite? B. What is the satellite's acceleration? Homework Equations I'm not sure but I believe we could possibly derive...
  38. N

    How do relativity explain elliptical orbits of planets?

    How do relativity explain elliptical orbits of planets?
  39. D

    How do we know the Sun orbits the Galaxy?

    How do scientists know that the Sun orbits the Milky Way? Is this something more ancient scientists knew or could have known hundreds of years ago?
  40. M

    Circular Orbits of a Black Hole

    In part, this thread is a tangential extension of an earlier thread entitled `Questions on Effective Potential`. However, this thread now moves the discussion in the direction of interpreting the results of the effective potential in terms of the circular orbital velocity, as derived from the...
  41. E

    What Are Hole & Open Orbits in Condensed Matter Physics?

    Homework Statement I am so confused about what a "hole orbit" is in condensed matter physics. I can identify it in the reduced zone scheme but what does it mean physically? Also, my book talks about open orbits which I am also confused about. Are open orbits subsets of hole orbits or are they...
  42. N

    Analysis of Electron Orbits in Magnetic Fields: Bravais Lattice

    Homework Statement IF we consider electrons in a crystal subject to a magnetic field. The electrons near the fermi energy wil obey open or closed orbits. Using semiclassical eqn of motion and band structure for a bravais lattice, discuss the behavour and derive all conserved quantities...
  43. D

    Why is the Earth getting closer to the sun and the moon getting farther away?

    We know that the Earth's orbit is gradually becoming closer to the sun, inevitably reaching a stage where it will collide with our star. Why shouldn't the moon behave in the same manner? Why is the moon actually moving away from the pull of the Earth every year? I have come to think that it...
  44. A

    Relating Distance and Speed for orbits

    Given just the distances from the sun of two comets for example, and the speed of one of the objects, how could one relate these two objects in order to find the speed the other object is traveling at?
  45. F

    Emission/Absorption and electron orbits

    Just a thought; if indeed electrons transit around the nucleus, shouldn't we see relativistic doppler shifting as their orbits will have them either receding away or moving towards us? Thus, shouldn't elemental spectral lines really exist as 'spectral bars' of measurable bandwidth using high...
  46. A

    Distance between 2 orbits of a black hole

    [SOLVED] Distance between 2 orbits of a black hole Homework Statement Hello. I am currently working on the black holes in the Schwarzschild metric, an exercise course asks me to calculate the physical distance between different orbits. d_{1} = distance betwenn 2M and 3M d_{2} = distance...
  47. M

    Discreteness of Electron Orbits: Elliptical Shapes?

    We know that orientations of electron orbit are discrete , what exactly do you mean by discreteness ,& also is there any particular shape of orbits like an ellipse ?
  48. M

    Space quantization of electron orbits ?

    The values of theta that represent the angle b/w orbital quantum no. (l) & magnetic field direction can never by pi or 0 deg as then the magnetic quantum no . will have non integral values & and also the direction of orbital quantum no . & magnetic field will be parallel which means the electron...
  49. K

    Gravitation and Circular Orbits

    Just a question about gravitation equations: Neglecting Earth's rotation, show that the energy needed to launch a satellite of mass m into circular orbit at altitude h is equal to: (\frac {GMm}{R})(\frac{R+2h}{2(R+h)}) Where R = the radius of the Earth and M = the mass of the Earth...
  50. K

    Gravitation and Circular Orbits

    Just a question about gravitation equations: Neglecting Earth's rotation, show that the energy needed to launch a satellite of mass m into circular orbit at altitude h is equal to: (\frac {GMm}{R})(\frac{R+2h}{2(R+h)}) Where R = the radius of the Earth and M = the mass of the Earth...
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