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. G

    Slowing down the earths rotation and changing the moons orbit

    I have a friend who believes that if he spins in a circle he is changing the angular momentum of the Earth and therefore is slowing down the Earth's rotation. Can someone explain exactly why this is not true? To me it is common sense, but I am no physics major. Also, the same friend is...
  2. K

    Saturn's Semi-Major Axis: Exploring the 10-Year Orbit

    Saturn takes about 10 years to go around the Sun once. What is the semi-major axis of Saturn's orbit?
  3. T

    Can you be in stable orbit inside a blcak hole?

    If you are in free fall inside a black hole, shouldn't it feel like normal space even though people on Earth saw you enter a black hole?
  4. B

    Force to keep a Object in Orbit

    How is it possible to calculate the force it takes to keep an object in a orbit This is not homework..
  5. B

    Calculating Min Δv for a Comet to Intersect Earth's Orbit

    Homework Statement A comet in a circular orbit around the Sun has speed v0 and radius r0 = aRE , where RE is the radius of the Earth’s orbit and α is a constant > 1. The comet has its velocity reduced by Δv in a collision that does not change its initial direction. Show that the...
  6. D

    Satellite following circular orbit.

    Homework Statement A satellite with a mass of 5.00 x 10^2kg is in a circular orbit, whose radius is 2r_e, around earth. Then it is moved to a circular orbit with a radius of 3r_e. a) Determine the satellite's gravitational potential energy from the first orbit to the second orbit. b)...
  7. M

    Moon orbit and conservation of energy

    I have seen this topic discussed a bit on the web, but I don't see any clear answers. I takes a lot of energy to make the moon go in a curve, if you had to do it with rockets you would need a lot of fuel. Therefore it takes a lot of energy to make the moon go round the Earth for 4 billion...
  8. R

    Do sattelites orbit with the rotation of the earth?

    Hey there, The other day i was solving a simple curvilinear motion problem that used a sattelite in orbit around the Earth as an example and it got me thinking. If a geostationary sattelite is always above the same region of the Earth (and can only occupy an orbit of a certain altitude) it...
  9. G

    Could the Chicxulub asteroid have changed Earth's orbit or axis at all

    I heard that the recent Chile earthquake moved Earth's axis by 8cm or so. Could the Chicxulub asteroid (or the even bigger, Antarctic one I just http://www.dailygalaxy.com/my_weblog/2010/03/did-the-planets-most-massive-asteroid-impact-ever-occur-in-antarctica-nasa-gravity-maps-point-to-yes.html"...
  10. B

    What happens to the height of the orbit?

    Homework Statement 1) A satellite is in circular orbit around the sun. Which requires the greater change in satellite's speed: to escape the solar system or fall into the sun? 2)Why does atmospheric friction increase the speed of a satellite in low Earth orbit? Homework Equations...
  11. G

    Differential Equation for the Orbit - Goldstein Chapter 3

    Hello, A question here about Classical Mechanics, Goldstein (Ed. 3) On page 87 you have expression 3.33 which goes something like \[ \frac{1}{r^2}\frac{d}{d\theta}\left(\frac{1}{mr^2}\frac{dr}{d\theta}\right)-\frac{l^2}{mr^3}=f(r) \] I appear to end up with \[...
  12. M

    Object in elliptical orbit around another object

    Homework Statement In a science fiction story, humans have built a large spherical spaceship for an interstellar journey of many generations; they have christened their ship Big Bird. The mass of Big Bird is 7.496×1011 kg (the mass of an aircraft carrier is about 10^8 kg). Most of Big...
  13. I

    Spin orbit interaction and LS coupling

    I hope someone can help me out here. I am having difficulty understanding what the difference is between the spin orbit interaction and LS coupling scheme in atoms. I know the spin orbit interaction (or spin orbit coupling) is due to the interaction of say an electron's spin with it's orbital...
  14. T

    Kepler's constant and average radius of orbit

    Homework Statement Given that Jupiter has a mass of 1.9x10^27 kg, and the sun has a mass of 1.99x10^30 kg: a) Calculate the value of Kepler's constant for Jupiter. b) If Jupiter's orbital period is 11.89 Earth years, calculate the average radius of its orbit. Homework Equations K...
  15. M

    Can Photons Orbit a Black Hole?

    I do have a question that bothers me for some days now. I'm not too sure how qualified it is, but my mind needs to be eased here. I understand, that it may be taken as a fact, that BHs cause enough gravity to make photons "vanish" behind the event horizon. So like with any stellar object...
  16. P

    Finding the Central Force Given the Orbit

    Homework Statement Homework Equations on image The Attempt at a Solution The first thing I did was use the second equation to get Theta dot = L/mr2 Which I then subbed into the first equation to eliminate Theta dot. Now I need everything in terms of r, and this is...
  17. H

    Satellite Orbit Problem what am I doing wrong?

    I have a satellite orbit problem I'm not quite understanding...any help would be appreciated. Homework Statement Suppose a spacecraft orbits the moon in a very low, circular orbit, just a few hundred meters above the lunar surface. The moon has a diameter of 3500 km, and the free-fall...
  18. C

    Expansion of Universe And Its Influence on Earth Orbit

    Assuming the expansion of the universe as a given fact, how does it influence orbits i.e. of the Earth around the sun or other planets in the solar system? Is it also usually included into the calculation of trajectories of space crafts (i.e. Pioneer, especially with regard to the Pioneer...
  19. P

    Is the force of gravity a function of a planet's orbit?

    Homework Statement Calculate the formula for the force of gravity in a universe where Kepler's 2nd law holds and a planet revolves around the sun with polar eq r = 1 + sin (theta). Theta = pi/2 is where velocity and position vector are perpendicular. Homework Equations Universal...
  20. L

    What is the radius of a heliosynchronous orbit

    What is the radius of a "heliosynchronous" orbit Homework Statement The Sun rotates approximately every 26 days. What is the radius of a "heliosynchronous" orbit, that is an orbit that stays in the same spot of the sun. Homework Equations r = ((GMT^2)/(4pi^2))^1/3 The suns mass is...
  21. S

    Understanding the Spin of Electron and Its Quantum Numbers

    According to spin quantum number, the spin value of electron pair is taken as +1/2 and -1/2. Why should we take only these values. I didn't understand what the spin of electron represents.
  22. T

    Tom and Jerry Space Travel: Calculating Speed & Weight

    Tom and Jerry decide to go space travel. They are in a spaceship traveling in a circular orbit completing one revolution in 12 hrs (43200seconds) a. Calculate speed of the spaceship relative to the centre of the Earth b. Calculate Tom's weight while he is in orbit around the Earth.
  23. K

    Close to C orbit around Earth and how time would be affected

    There is a nuance of special relativity that I cannot seem to grasp. This may be very similar to the twin paradox, so I am trying to find out what the critical points are. If I hop into my spaceship and orbit Earth at 0.995C for, say, 100 years, I will see Earth's clock progress at an...
  24. Philosophaie

    Orbit around the Galactic Center

    The Galactic Center of the Milky Way is about 25,900 light years away from the solar system. Its mass is 4.31E6*(Mass of the Sun). What I would like to know is what is the elliptical, circular, or etc orbit around the singularity especially the vector v and vector r. And if there is one, the...
  25. C

    Can we see nuclear explosion from orbit?

    As topic says Can we see Nuclear Explosion form orbit altitued? or even form space? Just curious.
  26. F

    Calculating Circular Polar Orbit Parameters and Fractional Doppler Shift

    Hii guys.I have this problem.Can anybody help me on this.tq Homework Statement A satellite is in a circular polar orbit at a height of 870 km, the orbital period being approximately 102 min. The satellite orbit passes directly over a beacon at sea level. Assuming an average value of...
  27. S

    How Does Orbital Eccentricity Affect Satellite Calculations?

    elliptical orbit question please help Homework Statement see attachmentHomework Equations 2a (average distance of satellite from central body) = A (aphelium) + P (perihelium) ME = KE + PE ME = -GMm/24 KE = .5mv^2 PE = -GMm/r ME orignall = ME final The Attempt at a Solution I tried to put ME =...
  28. B

    Why is the Earth hotter in July and cooler in January?

    We know that the Earth revolves around the sun in an oval orbit the sun occupies one of its centers On this basis, the distance from the sun is not constant and the land closest to the sun in Maicon on Jan. 3 and and be further from the sun on July 4, the difference between the two points...
  29. B

    Orbit Energy and Eccentricity Derivation

    Homework Statement Ok so take r' to be r dot.. i have E = 1/2m (r' ^2 + h^2/r^2) - A/r = E Energy equation for central force (inverse square) and r = l/(1+ecostheta) where l is the latus rectum.. need to derive the expression linking E and e i.e. E= A^2/2mh^2 (e^2-1) but can't...
  30. B

    How Long Does It Take an Asteroid to Orbit the Sun Compared to Earth?

    An asteroid is orbiting around the sun at a distance of 4.2x 1011 m. If the Earth orbits around the Sun at a distance of 1.5 x 1011 m with a period of 3.2 x107 s, what is the period of the asteroid? Im thinking it was 9.0 x 10^7 s ?
  31. K

    Calculating Electron Orbit Radius in a Magnetic Field

    Homework Statement An electron orbits in a 5.76 mT field with an angular momentum of 6.10 x 10-26 kg m2/s. What is the radius of the orbit (in m)? Homework Equations F = mv2/r F= QRB The Attempt at a Solution MV2/r = qrb v = wr so i plugged and my answer is still wrong .any help...
  32. M

    Closed Orbit of a Flow on a Manifold

    Homework Statement Let γ be a closed orbit of the flow φ on the manifold M and suppose there exists T>0 and X0 є γ such that φT(X0) = X0. Prove that φT(X) = X for every X0 є γ. Furthermore locate two closed orbits γ1 and γ2 and positive periods T1 and T2 for the flow of r ̇=r(r-1)(r-2); θ...
  33. J

    Understanding the Physical Significance of 'a' in Kepler Orbit Equation

    Sorry if this is in the wrong forum. I have the equation r = \frac{a(1-e^2)}{1+e \cos \theta} , and I'm wondering what the physical significance of the numerator is. More specifically, what is 'a' (since e is what it usually is)? I've seen various other representations with terms like...
  34. S

    Calculating Eccentricity for an Elliptical Orbit

    Homework Statement a satellite is set to orbit a planet of mass 4X 10^20 kg . It is placed at a distance of separation of 10^7m with a velocity of 30 degrees to the line connecting the center of the planet and the satellite. What will be its eccentrity fo orbit? (Answer is .89) Homework...
  35. S

    Geostationary orbit propagator

    Hi guys, I've been trying to make a longitude and drift rate propagator for a geostationary satellite but the equations do not take into account other perturbing forces apart from the Earth's triaxiality. Longitude = Initial Longitude + Initial Drift Rate * Elapsed Time + 0.5 *...
  36. A

    Orbit radius of 2 collided satellites

    Homework Statement Two satellites have mistakenly been put in identical Earth orbits of radius R. Satellite A with mass "m" is orbiting clockwise while satellite B with mass "2m" is orbiting counterclocwise. The two satellites have a head on collision and move as one body after the collision...
  37. S

    Annoying ellitpical orbit problem

    Homework Statement a planet in elliptical orbit about a star has speed of 100 m/s at its closest approach of 1X 10^10m . what is the speed at its furthest approach of 3X10^10m? What has happened to its total mechanical energy? Homework Equations The Attempt at a Solution
  38. S

    Conservation of ME and stable orbit

    Imagine a planet in elliptical orbit around a star, without any perturbation from third bodies and moving in perfect vacuum. The only force acting in the system is gravity. As the planet gets closer to the star, gravity acts in the direction of its motion, so it gains speed and KE but loses...
  39. B

    Time it takes for a satellite to orbit the Earth

    Homework Statement Determine the time it takes for a satellite to orbit the Earth in a circular "near-Earth" orbit. The definition of "near-Earth" orbit is one which is at a height above the surface of the Earth which is small compared to the radius of the Earth, so that you may take the...
  40. A

    Calculate Spin-Orbit Coupling in 19K: Estimate <(1/r)dV/dr>

    Homework Statement The 4p → 4s transition in 19K produces a pair of lines at 766.49nm and 769.90nm. Estimate the value of <(1/r)dV/dr> for the optically active electron in 19 K Homework Equations The Attempt at a Solution help needed urgently please. All i know so far is...
  41. M

    Magnetic field of a proton in circular orbit

    Protons having momentum 7.63*10^-16 kg*m/s are held in a circular orbit of radius 1 km by an upward magnetic field. What is the magnitude of the field? Answer in units of T (Tesla). r=mv/qB; where r is the radius of the circular orbit, m is the mass of the particle, v is the velocity of...
  42. S

    Speed update of a comet in an ELLIPTICAL orbit

    A comet is in an elliptical orbit around the Sun. Its closest approach to the Sun is a distance of 5e10 m (inside the orbit of Mercury), at which point its speed is 9e4 m/s. Its farthest distance from the Sun is far beyond the orbit of Pluto. What is its speed when it is 6e12 m from the Sun...
  43. S

    Change in speed around elliptical orbit

    A comet is in an elliptical orbit around the Sun. Its closest approach to the Sun is a distance of 5e10 m (inside the orbit of Mercury), at which point its speed is 9e4 m/s. Its farthest distance from the Sun is far beyond the orbit of Pluto. What is its speed when it is 6e12 m from the Sun...
  44. J

    What Caused the Change in Earth's Orbit 125,000 Years Ago?

    last night i was watching a public broadcasting special about climate change, and they mentioned that 125,000 years ago there was a large peak in CO2 in the atmosphere which caused a rise in global temp. they stated that the effect was caused by a "change in the Earth's orbit around the sun."...
  45. G

    Did Mars belonged in Earth's Orbit at one time?

    I am curious how easily my theory can be disproven... I have never heard anyone mention it, and as well I have no knowledge to support it. I was daydreaming of what would cause a planet simular to ours, to lose all of its elemental resources. It could be the fact that I am reading a book on...
  46. S

    Luanch angle to put a satellite in an orbit?

    I have a Question: suppose we have a satellite (m=400kg, V0=40m/s) and we want to put it in a 1000km orbit (r=1000km)...what should be the launch angle? P.S: is this question complete?(For Lack Of A Better Word) .. I mean do we have a formula which relates these parameters.. or perhaps a...
  47. E

    Tracking the Sun's Galactic Orbit: Uncovering the Origins of Our Solar System

    our suns galactic orbit?? Friends, I have always heard that it would be almost impossible to track the path of the sun through the galaxy. Yet I have come across this paper: ICE AGE EPOCHS AND THE SUN’S PATH THROUGH THE GALAXY D. R. Gies and J. W. Helsel Department of Physics and...
  48. K

    Putting a satellite into 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 30degrees to the local vertical. If M is the mass of the planet, show that (Vo)^2 = 5GM/4R. Assume...
  49. M

    How was the Earth's Orbit Derived?

    Could someone explain the idea, method of how Earth orbit was derived, in non-mathematical terms (well, some math is fine too)? I am more interested in the (ingenious) engineering/experimental approach behind it. I guess it's related to or requires the determination of Earth mass, and from the...
  50. A

    Speed of satellites in a geostationary orbit

    We're doing orbits and such in physics at the moment, and out teacher said "if a geostationary satellite gets further away, it has to go faster". I get this, because with a bigger orbit it would have to move faster to stay above the same point on earth, more distance to travel in the same time...
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