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. D

    Comet Orbit Astrophyiscs question

    Homework Statement "Supposing that at perihelion a comet is 1 Au from the sun and its speed at that point is 200km/s( in a frame of referance in which sun is stationary). Find its mean PE and KE to one sig digit. Does it satisfy the virial theorem? Homework Equations K= .5mv^2 U=-GMm/r...
  2. E

    Spacetime, curvature, orbit, matter and reactions

    In the BBC film Einstein and Eddington, Eddington describes the theory of spacetime using a table cloth (space), a loaf of bread (sun) and a piece of fruit (a planet). The Bread is placed in the middle of the table cloth, this forms curves in the cloth. He then takes a piece of fruit and...
  3. B

    Calculating Planet Deceleration Due to Decreased Gravity

    Let say gravity suddenly decreased 10%, - for instance due to tidal friction etc... How fast would a planet decelerate? - How can this be calculated?
  4. F

    Orbit of a star in a sherical potential

    Homework Statement A star is at radius r = 10kpc with v_t=100km/s and v_r=50km/s. The spherical potential is \phi = V^2ln(r) with V=200km/s 1. what is r_min r_max? 2. Integrate the orbit numerically The Attempt at a Solution 1. at r_min and r_max v_r is 0 therefore I can write...
  5. A

    Time average of potential energy in Keplerian orbit

    Hello, I'm trying to show that the time average of the potential energy of a 2-body system is equal to the instantaneous potential energy of that system when the two bodies are separated by a distance equal to the semi-major axis, a. So I know that U = \frac{-Gm_{1}m_{2}}{r} and the...
  6. R

    If a comet kicks the moon out of its orbit and away from earth

    If a comet kicks the moon, or any celestial object for that matter, out of its orbit and away from the earth, would it alter Earth's rotational axis?
  7. G

    Angle of the Sun above orbit plane on satellite-centered celestial sphere

    I'm trying to show that for certain combinations of altitude and inclination there will be periods of the year where a satellite has eclipse-free orbits. Using a satellite-centered celestial coordinate system, in which the orbit plane is the equator and the direction of Earth is fixed along the...
  8. B

    Capturing an asteroid in Earth orbit

    Yes I know someone else has posted something similar but I was wondering if capturing an 150 meter asteroid is possible in Earth orbit? Also can it be done by adjusting the delta v way out from Earth using the tug of a probe that you send to do such a job? (And maybe a final slow down with the...
  9. S

    How much mass does it take before photons will have a stable orbit?

    This is my first post so I hope I'm putting it in the right section :redface: I searched for similar questions but could not find one. Edington preformed his experiment where he observed the bending of light around the sun due to gravity. I have been thinking this past weekend about a...
  10. A

    How to calculate the required force necessary for orbit

    Hello, I am working on a software application which will require me to generate objects in orbit around other objects. Now, this is my belief, and I am asking for correction if I am wrong--- If given two objects, O1 and O2, with masses M1 and M2, and I want to make O2 orbit O1 at an...
  11. S

    The Atmosphere and Earth's Orbit (Probably Easy Q)

    Hi, just wondering about a (probably) easy queation. Was learning about the coriolis effect today and how since the atmosphere is not rigidly connected to the Earth it appears to veer off a northerly/southerly course in a direction depending what hemisphere it occurs in... etc. Basically its...
  12. Pengwuino

    First broadcast TV satellite's orbit

    I noticed on Modern Marvels that they mentioned sometihng about hte first satellite put up for broadcast TV transmission. I think. They mentioned it had an oblong orbit that allowed it to be within tranmission range for only 20 minutes every 24 hours. Why was this? Was there limitations back in...
  13. S

    Circular motion and parabolic orbit

    Homework Statement A point object of mass m is connected to an inertialess string of length L, the other end of which is connected to a fixed point O. At time t=0, the object is assumed to move horizontally in a vertical plane from the bottom point A (OA=L). in the clockwise direction with...
  14. DaveC426913

    Aboard the International Space Station: Who's in Orbit Now?

    Where can I find out who is currently aboard the International Space Station?
  15. Mentallic

    Satellite is in low orbit around the Earth

    I've read that if a satellite is in low orbit around the Earth, the increased friction due to the atmosphere causing the satellite to slow down and finally fall back to Earth. What if a large celestial body such as the moon is slowed down by some means? Will it eventually fall to Earth? I...
  16. G

    Circular orbit VS Elliptical orbit? Differences?

    Circular orbit VS Elliptical orbit?? Differences? Homework Statement Hi I am trying to understand some questions about Space and man made satellites...i would really appreciate it if someone could help me out thanks...also i included an extra question about the theory of relativity if you can...
  17. T

    Perturbing Accelerations in Satellite Orbit Determination

    Hi, first time posting here. I'm working on satellite orbit determination and wish to add in perturbing accelearations in addition to the Earth's graviatational field. I will be adding in acceleration due to the moon, sun, atmospheric drag, etc... The acceleration due to the Earth's...
  18. C

    Why haven't we launched any artificial satellites that orbit the Moon?

    I would've thought something like that would be do-able given we've landed on the moon, but also quite useful for discovering more about it.
  19. M

    What speed would a proton need to orbit in an exact circle ?

    Homework Statement Assume the Earth’s magnetic dipole moment is aligned with the Earth’s rotational axis, and the Earth’s magnetic field is cylindrically symmetric (like an ideal bar magnetic). What speed would a proton need to orbit in an exact circle around the Earth at a height of 476...
  20. Matterwave

    Conceptual GR question (regarding orbit paths)

    I'm by no means even adequate in the field of General relativity, so if my question is dumb, please excuse me. Anyways, so I know that from the EFE's you can get the metric for the space-time you are considering, and from this metric you can get the geodesics of this space-time using...
  21. daisey

    Electron Orbit: Exploring Kenneth W. Ford's Quantum World

    I am currently reading Kenneth W. Ford's book entitled "The Quantum World". In chapter 2 there is a section on Length, and in that section he talks about the size of atoms and electrons. He uses an analogy where the nucleus of a Hydrogen atom is the size of a basketball, and the electron...
  22. T

    Radius of Satellite Orbit - 2.1 Days Period

    Homework Statement A satellite orbits the sun with a period of 2.1 day. What is the radius of its orbit? Homework Equations T=2pi*r/V The Attempt at a Solution If the time is given in days I have to convert to seconds right? Also how would I find velocity would I use V=square...
  23. S

    Calculating Altitude for a Satellite in Synchronous Orbit with Saturn

    Homework Statement Satellite in synchronous orbit with equator of Saturn. Find altitude in km. rotational period = 38826 s radius of Saturn = 6.03E7 m mass of Saturn = 5.68E26 kg Gravity constant = 6.673E-11 Homework Equations T^2 = (4pi^2)(r^3)/(Gm) The Attempt at a Solution...
  24. R

    Seeking Stable Orbit: Investigating a Rigid Pole in Space

    Here's a thought that was bugging me last night: Lets say you placed a very long rigid pole (jokes kept to a minimum please) into orbit so that one end (end #1) faced the center of the earth, and the other (end #2) pointed out into space (So that the center of the Earth and all the points on...
  25. M

    Do Planets Orbit Closer to the Sun Over Time?

    Just a quick question Are the planets totaly locked in there orbits forever or do they slowly get drawn in closer to the sun?either by the sun's gravitational pull or simply by the sun expanding? Thanks in advance for any replys mike
  26. P

    Earth's Elliptical Orbit around the Sun

    By just knowing the clues like the force of attraction between two masses and angular momentum conservation principle , linear momentum conservation principle and geometry..can we derive the trajectory of the Earth around the sun is ellipse..if so please tell me your ideas..
  27. J

    Calculating Mercury's Orbit with Hyperbolic Geometry

    If this is in the wrong section, I apologize. I've been doing some independent research on the applications of hyperbolic geometry, and I ve hit a rather difficult snag. I've seen in a few places on line that Mercury's orbit can be more accurately calculated using hyperbolic geometry as...
  28. T

    Charge moving in cyclotron orbit

    Homework Statement The particle moves in a plane perpendicular to the magnetic field direction as shown in the figure. What is omega, the angular frequency of the circular motion? Express omega in terms of q, m, and B_0. Homework Equations omega=2pi/T The Attempt at a...
  29. G

    Spin orbit coupling/orbital degeneracy

    disregarding the hyperfine structure and the lamb shift for the moment, spin orbit coupling says that 2S1/2 and 2P1/2 have the same energy. do 2S0 and 2P0 have the same energy? if 2P splits into 3/2 and 1/2 does the 3D orbital split into 5/2, 3/2, and 1/2 and the 4F orbital into 7/2, 5/2, 3/2...
  30. K

    Thrust needed for Orbit of a satellite

    Homework Statement A satellite is fitted with a station keeping rocket capable of producing thrust of 500N. Its speed is 500Km/hr. Mission control wishes to increase the radius of orbit by a factor of 0.5. For how long should the rocket be fired to achieve this? (The weight of the satellite...
  31. C

    Moving an asteroid into Earth orbit

    Suppose we want to use an asteroid to build a large space station. We could alter the course of a asteroid so that it will come very close to Earth, but the velocity relative to Earth will then be more than the escape velocity of 11.2 km/s. Presumably we must use aerobraking to let it lose...
  32. Y

    How does the Satellite manage to stay in earth's orbit?

    I have read that an object needs to have a velocity of around 8km/s to not fall back on Earth and to stay on orbit. Based on the above, are all our human made sattelites constantly traveling at around 8km/s to not fall back on earth? Is so doen't it need a lot of fuel? Does it store all this...
  33. K

    How Do You Calculate the Period of a Spacecraft's Elliptical Orbit?

    Homework Statement Consider a spacecraft in an elliptical orbit around the earth. At the low point, or perigee, of its orbit, it is 400 km above the Earth's surface; at the high point, or apogee, it is 4000 km above the Earth's surface. 1. What is the period of the spacecraft 's...
  34. O

    Period of Orbit Homework: Calculating Satellite Revolution Time

    Homework Statement What is the period of revolution (in minutes) of a satellite orbiting Earth at 161000 m? Homework Equations T^2 = (4*pi*r^3)/(GM) The Attempt at a Solution Well, I plugged in the values, and got T = 5250.925844, but that's not right. T, would come out as seconds...
  35. P

    Delat energy required to excite hole from lowest energy orbit to valence band?

    Delta energy required to excite hole from lowest energy orbit to valence band? I have calculated the orbit of a hole in its lowest energy orbit, but am struggling to work out \delta\epsilon (energy needed to excite it to valence band). Any help much appreciated.
  36. C

    Energy to put space shuttle in orbit

    Homework Statement The space shuttle orbits about 300km above the surface of the Earth. The shape of the orbit is circular and the mass of the space shuttle is 6.8*104kg. The mass of the Earth is 6.0*1024kg and the radius of the Earth is 6.4 *106m. Calculate the energy needed to put the space...
  37. P

    Question about space junk in orbit

    I did not know where else to post this question but put it here since it is more related to mechanics than to astronomy. I am curious as to why small bits of space junk (bolts for example) are traveling so fast around Earth that they could poke holes in the International Space Station. Are...
  38. A

    Deriving an expression for the radius of a satellite's orbit around Earth(?)

    Homework Statement Derive an expression for the radius of a satellite's orbit around Earth in terms of the period of revolution, the universal gravitation constant, and Earth's mass. Homework Equations The final equation should be: r = \sqrt[3]{\frac{T^{2}Gm_{E}}{4\prod^{2}}} The...
  39. U

    Calculating Orbital Speed: Jupiter & Earth Orbit Time

    ok just a couple orbital questions I forget the equation that needs to be used and do not have my textbook with me so if anyone knows the equation for finding orbital speed that would be great! 1. calculate the speed of a satellite in orbit 9.5 x10^3 km above jupiter. radius of Jupiter =...
  40. F

    Eliptical Orbit and Eccentricity

    1. Problem statement The space shuttle is in circular orbit of radius R around the earth. The pilot triggers a brief burn that imparts a forward impulse 'p' to the shuttle. After the burn, the shuttle is in an elliptical orbit which passes back through the point where the burn took place once...
  41. S

    Relativistic Particle in Circular Orbit

    Homework Statement A particle of charge q and rest mass m0 moves in a circular orbit of radius R and angular frequency w in a uniform magnetic field b in the z direction: Find b in terms of R,q , m0, and w. Homework Equations b = (1/c) v X e and v = w/R and e = not sure. My problem is...
  42. A

    Determine the radius of the electron's orbit

    pleasez,,,heeeeeelp me In a simple model of the hydrogen atom, the electron revolves in a circular orbit around the proton with a speed of 2.2*10^6. Determine the radius of the electron's orbit?
  43. P

    Finding the minimum speed for putting an object in orbit

    yet another doubt about gravitation. we must affirm that it's also not a homework question, so, we won't need any number, only the formulas. Homework Statement 1) suppose that an object is located in a distance r from the center of the Earth (not necessary to say that r is larger than the...
  44. T

    Calculating the Semimajor Axis of Pasachoff's Orbit

    Homework Statement The asteroid Pasachoff orbits the Sun with a period of 1417 days. What is the semimajor axis of its orbit? Determine from Kepler's third law, using Earth's orbital radius and period, respectively, as your units of distance and time. ans : _______ km Homework...
  45. G

    What would happen to Earth's orbit if it increased in mass or lost velocity?

    Would it begin to spiral into the sun or would it slip into a new orbit? Don't most meteorite impacts occur due to the Earth sweeping into the meteor like a car hitting bugs? Wouldn't each and every impact slow the Earth down a tiny bit while also adding to the mass of the planet? I...
  46. H

    The Mystery of Satellite Speed: Solving an Elliptical Orbit

    Homework Statement A satellite is in an elliptical orbit at altitudes ranging from 230 to 890 km. At the high point it's moving at 7.23 km/s. How fast is it moving at the low point? I would think i would have to use some sort of energy conservation equations. but i really don't know where...
  47. R

    Binary Stars: Equal Mass, 350 Million km Separation, 5.4 Earth Years Orbit".

    Suppose that a binary-star system consists of two stars of equal mass. They are observed to be separated by 350 million {\rm km} and take 5.4 Earth years to orbit about a point midway between them. I got 1.1x10^29 as my answer, but it is incorrect. Can anyone help me out?
  48. G

    Calculating minimum energy to remove satellite from orbit

    Homework Statement A satellite of mass 4500 kg orbits the Earth in a circular orbit of radius of 7.6 x 10^6 m (this is above the Earth's atmosphere).The mass of the Earth is 6.0 x 10^24 kg. What is the speed of the satellite? What is the minimum amount of energy required to move the...
  49. qntty

    How can I track Earth's distance to the sun on a specific date?

    A few weeks ago I saw a web page (I believe it was at NASA) that allowed you to enter a date and see Earth's distance to the sun on that date. I searched but can't find the site again, does anyone know where I can find this page?
  50. M

    Electron orbital frequency of hydrogen atom if given orbit radius

    Homework Statement In a classical model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. A) What is the electron's orbital frequency? Homework Equations F = qE E= kq/r^2 angular velocity = v^2/r The Attempt at a Solution I'm...
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