Orbits Definition and 498 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. A

    Find Smallest Eccentricity for Intersecting Orbits

    Homework Statement Two masses, m and 2m, orbit around their CM. If the orbits are circular, they don't intersect. But if they are very elliptical, they do. What is the smallest value of eccentricity for which they intersect? Homework Equations...
  2. S

    How Does Eccentricity Influence Orbital Speed Ratios in Planetary Motion?

    Homework Statement A planet has an eccentricity of 0.006800 and a semimajor axis of 0.7233 AU, find the ratio of ortibal speed at perihelion to that at aphelion. Homework Equations d=e x a L=mvrsin\theta The Attempt at a Solution I plugged in and solved for the distance between...
  3. E

    For (x,y) in R2, describe the set of orbits geometrically.

    Homework Statement 4a) If x, y are in R, prove that (R, +) acts on R2 by (x,y)*r = (x+r, y) for all (x,y) in R2 and for all r in R. b) If (x,y) are in R2, find the orbit of (x,y). Describe geometrically. Homework Equations none that I can think of The Attempt at a Solution The...
  4. E

    Show the group action on (x, y) and, desribe the orbits.

    Homework Statement 1 a) Prove that the group (nZ, +) acts on Z by a*g = a + g for all g in nZ and for all a in Z. b)What are the orbits? c)How many orbits are there? Do the set of orbits remind you of anything in number theory? Homework Equations not sure The Attempt at a Solution...
  5. P

    Orbits of planets/Angular momentum

    Homework Statement Show that the angular momentum in circular orbit around a mass M can be written as functions of just the masses, the orbit radius, and G. Homework Equations L = r x p = r x mv L = Iw The Attempt at a Solution I had no trouble showing that the total...
  6. F

    Gravitational Orbits: Circular vs. Elliptical

    Homework Statement 1. Which of the following statements about a circular orbit are true? (The planet is orbiting around the star.) a. At any instant the momentum of the planet is tangent to the planet's trajectory. b. The magnitude of the planet's momentum is constant. c. At every...
  7. F

    Gravitational Orbits: True Statements about Circular & Elliptical Orbits

    1. Which of the following statements about a circular orbit are true? (The planet is orbiting around the star.)a. At any instant the momentum of the planet is tangent to the planet's trajectory. b. The magnitude of the planet's momentum is constant. c. At every instant, dvector p/dt points...
  8. F

    Formulas for Elliptical Orbits X,Y,Z Co-Ordinates

    Can someone tell me what the formulas are for the x,y & z co-ordinates of a planet on its elliptical orbit of the sun? I don't mind astronomy terms (I'm no expert on them but have a basic knowledge and will look up and learn any I don't know). It's not homework, just something that's doing...
  9. R

    Are De-Broglie & Bohr's Stationary Orbits Different?

    Are De-Broglie stationary orbits different from Bohr's stationar orbits? I really haven't been able to figure out.
  10. E

    E of Parabolic & Hyperbolic Orbits: Explained

    Homework Statement Show the the total energy of a parabolic is zero. Show that the energy of a hyperbolic orbit is positive.Homework Equations r=\frac{L^2}{GM\mu^2*(1+e cos\theta)} v^2=GM \left (\frac{2}{r}-\frac{1}{a} \right )The Attempt at a Solution E=T+U=\frac{1}{2}\mu v^2 -\frac{GM\mu}{r}...
  11. T

    Planet Orbits, finding radius HELPP

    Planet Orbits, finding radius HELPP! Homework Statement The planet Mars has a mass of 6.418*1023kg and completes an orbit around the sun in 687 days. The sun has a mass of 1.99 * 1030kg. what is the average radius of the orbit of mars? Homework Equations Force Gravity = G*(m1m2)/r2...
  12. K

    TA 2019 Physics 1 Question 5: Geosynchronous Orbit

    Homework Statement Communications satellites are placed in a circular orbit where they stay directly over a fixed point on the equator as the Earth rotates. The radius of the Earth is 6.37 x 106m, and the altitude of a geosynchronous orbit is 3.58 x 107m. What are (a) the speed and (b) the...
  13. 3

    The size of the orbits of a finite normal subgroup

    Homework Statement Let H be a finite subgroup of a group G. Verify that the formula (h,h')(x)=hxh'-1 defines an action of H x H on G. Prove that H is a normal subgroup of G if and only if every orbit of this action contains precisely |H| points. The Attempt at a Solution I solved the first...
  14. 3

    Orbits of a normal subgroup of a finite group

    Homework Statement If G is a finite group which acts transitively on X, and if H is a normal subgroup of G, show that the orbits of the induced action of H on X all have the same size. The Attempt at a Solution By the Orbit-Stabilizer theorem the size of the orbit induced by H on X is a...
  15. J

    Changes in planet orbits as a star (eg. the Sun) decreases is mass.

    Hi, I'm actually a Design Engineer but I find the topic of Relativity extremely interesting and I was wondering if somebody could give me some guidance on this. If Planets and Stars (due to their mass) 'warp' Space-Time then this means that our Sun distorts the fabric of space just like a...
  16. C

    Understanding the Orbit of Kapler's Law and its Relation to Potential Energy

    Hello, In question 3(b) in the following file http://phstudy.technion.ac.il/~wn114101/hw/wn2010_hw09.pdf Why the orbit will be a straight line? I think that when the particles are coming to r=0 the potential will be infinity, isn't that so? So the energy will be infinity and e will be...
  17. J

    Sun Vanishes - How Long Till Orbits Change?

    I've wanted to know this for 15 years. If every particle in the sun simultaneously tunneled to another galaxy, how long would it take the Earth to stop orbiting as if the sun were there? 0 seconds? ~7 minutes? Why? How fast does space-time un-deform?
  18. M

    Why do stars orbit around a spiral galaxy in a rosette shape?

    I am having trouble understanding how stars orbit around a spiral galaxy. First off, my understanding of the Local Standard of Rest (LSR) is that it is a point which corresponds to the average velocity of all the stars in the defined local neighbourhood. This point moves around the centre of...
  19. M

    What Do Epoch J2000.0 Orbital Elements Tell Us About Earth's Orbit?

    Can someone please help me with this? Epoch J2000.0 refers coordinate systems to the mean equinox and mean ecliptic of January 1, 2000, noon TT. I have the following mean orbital elements for Earth with element date January 1, 2000 and referred to j2000.0 epoch. a :=...
  20. R

    Calculating Final Speed of Engine-less Space Capsule Launched from Earth

    You launch an engine-less space capsule from the surface of the Earth and it travels into space until it experiences essentially zero gravitational force from the Earth. The initial speed of the capsule is 18,500 m/s. What is its final speed? Assume no significant gravitational influence from...
  21. C

    Universal gravitational, elliptical orbits

    1. Homework Statement a spacecraft of mass 1000kg, in an elliptical orbit about the earth, at one point its distance from Earth is 1.2 x 107 meters and its velocity is 7.1 x 103 meters per sec, and the velocity vector is perpendicular to the line connecting the center of the Earth to the...
  22. C

    Universal gravitational, elliptical orbits

    Homework Statement a spacecraft of mass 1000kg, in an elliptical orbit about the earth, at one point its distance from Earth is 1.2 x 107 meters and its velocity is 7.1 x 103 meters per sec, and the velocity vector is perpendicular to the line connecting the center of the Earth to the...
  23. C

    How To Find Angular Momentum of Elliptical Orbits

    Hey there is one question I have that has been burning in my mind. I know that in elliptical orbits of satellites/ spacecraft s/planets around a planet, angular momentum and energy is conserved, but how do we find that angular momentum only knowing the velocity of the orbiting object, its mass...
  24. E

    In 4-D, the Earth orbits around the sun in a straight line

    "in 4-D, the Earth orbits around the sun in a straight line" someone told me that in 4-D, the Earth actually orbits around the sun in a straight line, could someone try to explain to me how this is so? thank you
  25. M

    Newtons theory of gravity : satelite orbits and ellipses

    The figure shows two planets of mass m orbiting a star of mass M. The planets are in the same orbit, with radius r, but are always at opposite ends of a diameter. This is the equation eq. I used: mv^2/r=GMm/r^2+Gmm/(2r)^2 This is what I came up with but it is not the right answer. Where...
  26. PrincePhoenix

    The shape of our solar system's orbits.

    What's the shape of the planets orbiting the sun in our solar system according to this website http://www.chacha.com/question/what-is-the-shape-of-orbit-of-planets they are elliptical. But in a documentary (maybe history channel's "The Universe", but I'm not sure) I heard that our solar system...
  27. S

    Why Do Revolving Bodies Have Elliptical Orbits?

    Why revolving bodies have their orbits elliptical and not perfectly circular (please correct me if I am wrong)?
  28. A

    Elliptical orbits and focal points

    I was recently studying elliptical orbits and the precession of the perihelion of Mercury. I remembered from my pre-calc class that all ellipses have two focal points. In this case the obvious would be the Sun as on focal point for all the planets, but where would the second be? I have a...
  29. C

    Geosynchronous Orbits: Explaining Relativistic Motion

    I was having trouble making sense of the geosynchronous orbits from a relativistic point of view. Correct me if I am wrong, but in a geosynchronous orbit the object appears to hover over a certain place on the Earth, from the point of view of the Earth, which can be said to be at rest according...
  30. C

    How Do Neutron Stars Create Pulsars?

    Homework Statement Mostly a bunch of extraneous information, so feel free to skim: Large stars can explode as they finish burning their nuclear fuel, causing a "supernova". The explosion blows away the outer layers of the star. According to Newton's third law, the forces that push the...
  31. C

    Exploring the Connection Between Right Cosets and Orbits

    I'm just wondering if there is some sort of relationship between right coset and orbit of x. We just got to cosets, and it seems like the properties of cosets are eerily similar to orbits.
  32. G

    Elliptical Orbits velocity and distance

    This question is of an elliptical orbit with v1 ant its distance r1 and a second v2 with distance r2 located a different point in the elliptical orbit Which general relation connects the speed vi of the satellite and its distance ri from the center of mass of the planet at any two arbitrary...
  33. T

    Understanding homoclinic orbits

    Hey all, Can someone please tell me why is the trace of the Jacobian of an integrable hamiltonian system equall to zero on the homoclinic / seperatrix orbit ? Cheers, Thrillhouse
  34. B

    Please help: astronomy questions about how earth orbits the sun

    Below are some questions. I have struggled with these questions so any help would be greatly appreciated. Thank you so much. The Earth orbits the Sun: a. in a perfect circle b.in an ellipse with the sun at the center c.in an ellipse with the sun at the focus d.in a shape...
  35. G

    Planetary Orbits: Decay or Spiral?

    So, the moon goes around the earth, the Earth orbits the sun etc... Are the orbits eventually decaying orbits? That is, given enough time, will the moon hit the earth, Earth go into the sun etc...?? Is that why galaxies are spiralling?
  36. L

    What Are the Inclinations of Planetary Orbits Relative to the Sun's Equator?

    Does anyone know the inclination of each planetary orbit (in degrees) with respect to the plane of the Sun's equator-plane?All planetary inclinations are known with respest to the ecliptic, and the ecliptic's inclination is known with rescpect to the Sun's equator (7.25 degrees). Such data...
  37. R

    Why Are Orbits Elliptical? Rules of Circular Motion

    Hi Can someone explain why orbits are elliptical and not circular? Does elliptical orbits still follow the rules of circular motion (ex. constant centripetal force)? Thanks for any help that you can provide
  38. S

    Floating in Space: Can Humans Create Their Own Orbits?

    This question came to me as having an obvious answer yet I don't know. If a human is floating in space they bend spacetime themselves and could technically have small stuff orbit them. Sorry for the dumb question; just been bothering me. thanks for any help
  39. Evo

    Why Does the Newfound Planet WASP-17 Orbit Backward?

    I was speaking with a friend about this today, I don't see a thread on it. http://www.msnbc.msn.com/id/32391095/ns/technology_and_science-space/
  40. L

    What Units Should I Use to Calculate Planetary Orbit Time?

    Hi all, I'm working on a problem where I have to find the time it takes for a planet to form from a protoplanetary disk, using the equation: t = \frac {3}{A}M^{1/3} Where A= ( \frac {(1+2\beta)\sigma}{P}) (\frac {3\pi^2}{4\rho_m})^{2/3} However, I'm not sure which units the...
  41. F

    Comparing Planetary Orbits & Rotations in Pictured Figures

    I want to know the difference between the 2 types of rotations shown in the picture attached . planetary orbiting are similar to the second figure in the picture attached , all i want to know what is the difference between the 2 figures .
  42. K

    Electron Orbits and Nuclei 2- Rotation vs Orbital Motion

    1-is electron orbit about the nucleus ? 2-is there is different between rotation and orbit? thanks in advance
  43. S

    What is the other focus in an elliptical orbit?

    Hello. I've read in many books that the orbits of the planets of our Solar system are ellipses. With the one Focus as the Sun. Well, what is the other one? I mean every ellipse has two focuses...
  44. A

    Quantization of Orbits: Explained

    hi there we know that electrons around the nucleus in an atom can only exist in certain discrete energy levels (orbits) and that they can jump from one energy state to a higher one or a lower one. where is the electron when it is jumping from a higher stste to a lower state if it cannot exist...
  45. D

    Is There a Preferred Plane for Satellite Orbits?

    This is nothing so involved as the actual mechanics of orbit. I'm just curious, is there a preferred plane that satellites orbit in? I ask because on my frequent stargazings, after my eyes are VERY well adjusted to the dark, I can see what I assume to be satellites moving pretty quickly across...
  46. D

    Universal gravitation + orbits question

    Homework Statement A 450kg satellite is to be placed at an altitude of 2.45 x 10^6m above the Earth surface. Calculate the period the satellite will have when orbiting at that altitude. Homework Equations m2g = Gm1m2/R^2 = m2v^2 = m2(4pie)^2 R /T^2 = m2 2pie v/T Ac=4pie ^2 R / T^2...
  47. E

    What Defines Unstable Versus Unbound Orbits Around Black Holes?

    Hello, What is the difference between an unstable and an unbound orbit of a particle around a black hole? As far as I understand, an unbound orbit is (informally) a trajectory which does not represent a closed curve (such as an ellipse) around the black hole, and this condition formally...
  48. Z

    Calculating Length of Closed Orbits: Gutzwiller Formula & Hamiltonian Systems"

    given a Hamiltonian H=p^2 + V(x) how can you calculate the length of the closed orbits ? , i mean in gutzwiller formula you must perform a summation over the length of the closed orbits to calculate density of states g(E) but how can you know what the lenghts are ?? .. of course for Harmonic...
  49. A

    How Did Planets Enter Their Orbits?

    This is something I thought about while drifting off to bed last night. Immediately after the period between the big bang and the formation of planets, how did these newly created planets enter their respective orbits. I'm assuming the planets had different masses and that this was a...
  50. E

    Calculating Fuel Requirements for Geosynchronous Orbit | NASA Mission"

    Homework Statement NASA has a mission to put a satellite into an equatorial geosynchronous orbit, so that its orbital motion will keep it above longitude 150 as the Earth rotates beneath it. This is done in three steps: 1) The satellite is placed into a circular equatorial orbit 220 miles above...
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