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. M

    Find eccentricity of orbit of comet

    Homework Statement Find eccentricity for: a comet with mass 1.2x1010kg moves in an elliptical orbit around the sun. Its distance from the Sun ranges between .5AU and 50 AU. Homework Equations The Attempt at a Solution I drew it out to try and viualize it and i know eccentricity...
  2. S

    Problems with an Orbit: Eccentricity, Inclination, and Other Peculiarities

    Problems with an Orbit... Homework Statement what is peculiar about the orbit" Semimajor axis = 5740km Eccentricity = 0.1 Inclination = 53 Right ascension of the ascending node = 345 Argument of perigee = 270 True anomaly = 183 Homework Equations The Attempt at a Solution...
  3. J

    How far above the earth's surface is the satellite orbit?

    Homework Statement A. Suppose you are at the Earth's equator and observe a satellite passing directly overhead and moving from west to east in the sky. Exactly 15.0 hours later, you again observe this satellite to be directly overhead. How far above the Earth's surface is the satellite's...
  4. kreil

    Spacecraft orbit homework problem

    Homework Statement Suppose a spacecraft of speed v_c is in a circular orbit around the Earth at a height H from the surface of the earth. The rocket motor is fired in the opposite direction of motion to reduce the satellite's speed to v_0 and make the orbit elliptical. Let R denote the...
  5. F

    Equation of an Elliptical Orbit for a Moon around a Planet

    I am kind of new to astronomy and I have a few questions.. I need to be able to determine an equation expressing the elliptical orbit of Oberon around Uranus. I have four nights of data showing Oberon in different positions relative to Uranus. I am able to calculate the RA and Dec for both...
  6. D

    Orbital energy required to change a comets orbit

    Homework Statement Use the information in Section A.3 and the data in Table A.19 to calculate the heliocentric radial distance (in AU) of Comet Halley at 12h UT on July 16, 1994. - Done, Section A.3 just talked about finding dates using Epochs and such. Table 19 had comet details which will...
  7. B

    Period of satellite in circular orbit

    Homework Statement Given: G = 6.67259 × 10−11 Nm2/kg2 The acceleration of gravity on the surface of a planet of radius R = 4190 km is 6.5 m/s2. What is the period T of a satellite in circu- lar orbit h = 14120.3 km above the surface? Answer in units of s. Homework Equations...
  8. L

    Do electrons stay in orbit around the nucleus in the same way

    We stay in orbit around the sun? Our own planet's kinetic energy keeps it from succumbing to the Sun's gravity, same concept with the electrons, this time Gravity being electromagnetic force right? Edit: Damnit, wrong section...
  9. V

    Orbit of Moons & Shapes of Planets due to Warped spacetime

    First post, I am just a layman, so go easy. The way I understand it, the moon is following a straight line through space. However, the mass of the Earth is so great that it warps the fabric of spacetime and it appears that the moon is going around the earth. Same with any moon or planet, they...
  10. R

    Why Earth's Orbit is Elliptical

    Why Earth's orbit is elliptical rather than being perfectly circular
  11. M

    What is the orbit of 1 in the permutation group G?

    If G is a permutation group acting on a finite set A and x \inA, then |G| = |\Delta(x)| |Gx| where \Delta(x) denotes the orbit containing x. I'm having some difficulty understanding this theorem. For example, Consider the following set G of permutations of the set M = {1,2,3,4}...
  12. D

    Changing Orbit Angle for 3D Atom Model | Simple Question for Math Pros

    "simple" 3d orbit question Hi folks, I am following this pattern: http://www.bit-101.com/tutorials/3D-rotation.html to build a 3d model of an atom, using silverlight. I have what i think is an easy question for math pros... I'd like to know what I can change to make the angle of the...
  13. nukeman

    *Quick moon question - (about orbit)

    Is the Moon’s orbit more or less elliptical than the Earth’s? How does this affect the range of angular sizes for the Moon vs. the Sun? I always thought smaller objects are less elliptical than larger objets, so the moon would be less elliptical Can someone clarify? Thanks!
  14. nukeman

    Is Earth’s orbit far from circular?

    Of course Earth's orbit is not circular, but Is Earth’s orbit far from circular? Thanks
  15. O

    Using Momentum & Energy Principles to Analyze a Satellite Orbit

    In certain cases, using both the momentum principle and energy principle to analyze a system is useful, as they each can reveal different information. You will use the both momentum principle and the energy principle in this problem. A satellite of mass 4000 kg orbits the Earth in a circular...
  16. T

    Calculating Work with Kinetic Energy in Orbit

    Homework Statement A 62kg satellite orbits the Earth with a radius of 3.3*10^7 m. A net external force acts on the satellite to an orbit of 7.7*10^6 m, what work must the external force do? Homework Equations W = integral of F with respect to d The Attempt at a Solution Integrate...
  17. M

    Distance to Geosynchronous Orbit

    How do you calculate the distance above the surface of the Earth to geosynchronous orbit.
  18. E

    Speed of orbiting planet given eccentricity of orbit

    Homework Statement If the eccentricity of a planet's orbit about the sun is 0.4, find (a) the ratio of the lengths of the major to minor axes of the planet's orbit, and (b) the ratio of the speeds of the planet when it is at the ends of the major axis of its elliptical orbit. Homework...
  19. C

    Understanding Centripetal and Gravitational Forces in Orbital Motion

    I'm having some trouble understanding this (not a homework question by the way.) A satellite orbits the Earth with a certain angular velocity. Centripetal acceleration is directed radially inward. Acceleration due to gravity of the Earth is also directed radially inward. If I draw a free body...
  20. C

    Total energy of satellite in orbit

    Homework Statement The weight of a satellite in a circular orbit round the Earth is half of its weight on the surface of the Earth. If the mass of the satellite is 800kg, determine (i)the altitude of the satellite (ii)the speed of the satellite in the orbit (iii)the minimum energy required...
  21. F

    What is the Radiance of Solar Radiation at Earth Orbit?

    Homework Statement given that T(sun)=5771.4, S(Earth)=1370, D(Earth)=1.5x10^8km, R(sun)=7x10^5km calculate the radiance of solar radiation at Earth orbit Homework Equations Irradiance=Radiance/Solid Angle Solid Angle=Area/Distance^2 I=sigma*T^4 The Attempt at a Solution...
  22. I

    Why does a4n electron need to move in an orbit?

    Note: This isn't a HW question. I have learned that the magnitude of charge of a proton and electron is the same (i.e. 1.602 * 10^19 Columbs). Then why does an electron need to move in an orbit because the charges could cancel each other out and the electron could remain stationary. I...
  23. S

    Circular Motion of earth's orbit Problem

    Hello everyone! Please, help me understand the following problem: Homework Statement Earth's orbit around the Sun is nearly circular. The period is 1 yr = 365.25 d. (a) In an elapsed time of 5 d, what is Earth's angular displacement? Solved! (b) What is the change in Earth's velocity, Δv...
  24. C

    How Does Satellite Velocity Change with Altitude?

    Homework Statement The problem is that a satellite is ejected from a planet radius R and mass M, that has no atmosphere, 30 degrees from vertial with velocity vo. This is a multi part problem dealing with center of mass/inertia, the part I need help with is the following: 1. When the...
  25. U

    Escape velocity when in earth's orbit

    I have a problem where it ask to find the period/time(using Kepler's 3rd law) of an unpowered spacecraft to move from Earth's orbit to Mars orbit using the transfer orbit approach. I found P/T using kepler's 3rd law but the second part ask to find how fast the spacecraft need to be moving at...
  26. C

    Calculating Orbit Velocity Around a Star

    I'm toying with the idea of making a little 2D space orbiter game so I've implemented Newton's universal gravity law into this little app. It works really well, even. The problem I'm having is when I want to create an asteroid-belt. I spawn little asteroids randomly around an area around the...
  27. W

    G must have an element with no fixed point when there is only one orbit

    I am studying for a modterm on Monday and asking for help on the homework questions I got WRONG on my problem sets (so I can hopefully improve my understanding and see my mistake). This is my reworked version of the incorrect HW problem and I would like to know if I am on the right track...
  28. M

    Looking for data on the orbit of S2 star

    Hello, I'm doing a project on proving the existence of black holes. I am using Sgr-A as a test subject and am after the data set for the orbit of the star S2 around it so I can do some of my own calculations on it. Does anyone know where i might be able to obtain these?
  29. N

    Will electrons fly out of atoms and planets lose orbit?

    Hello, I'll take you've heard of the heat death of the universe. Now I was wondering: will electrons actually, at some point, leave their atom? If so, is this solely due to the fact that the quantum mechanical chance of an electron being out of an atom is not zero and thus, according to...
  30. K

    Astrophysics - elliptical orbit proof help.

    A.) Assume a rectangular coord system has its origin at the center of an elliptical planetary orbit and that the coord system x-axis lies along the major axis of the ellipse. Show that the equation for the ellipse is given by x^2/a^2 + y^2/b^2 =1. where a and b are the lengths if the...
  31. L

    Welcome! Ask Away: How Electrons Orbit Without EM Waves

    Hi Everyone! I'm new here and like this forum. Can anyone tell me how the electron moving roundly in atom doesn't emit EM waves while changing it's speed?
  32. S

    Traveling at the speed of light in orbit around a black hole

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  33. M

    Angular Momentum: Keeping Planets on their Orbit

    Hy. What makes the planets to keep their position on the orbit (the same orbit). Shouldn't be attracted by the gravitation of the star ? Thanks!
  34. Q

    Calculate the time required in millions of years for one orbit.

    Homework Statement The solar system is situated 26,000 light years from the centre of our galaxy, the Milky Way, and it orbits the centre at a speed of 220 km/sec. Calculate the time required in millions of years for one orbit. (NOTE: The circumference of a circle = 2 pi r where r is...
  35. M

    Are astronauts weightless in orbit?

    Homework Statement If someone told you that astronauts are weightless in orbit because they are beyond the pull of gravity, would you accept this statement? Explain. Homework Equations The Attempt at a Solution I say no. There is still gravity, but its just weaker with distance...
  36. P

    Doubt about the polar equation of a Kepler orbit

    Good morning, I have a doubt about the differentiation of the polar equation of an orbit: r=\frac{p}{1+e\cos\nu} It represents the relative position of a planet with respect to the central body. Here, p is the parameter, e is the eccentricity and r is the radius of the planet measured from...
  37. Philosophaie

    Tracking Unstable Elliptical Orbits for College-Educated Scientists

    A satellite is in an unstable elliptical orbit around the earth. Is there a way of tracking each satellite's orbit till it reaches the critical stage then follows it's reentry path? V<Vescape r=a*(1-e^2)/(1+e*cos(True Anomaly)) Book recommendations welcome. College educated.
  38. Q

    Why do all the planets orbit in the same plane?

    Hello, I was just curious why do all of the planets in the solar system orbit in approximately the same plane? Why is it not random? This is not a homework question, but if possible I would like to see the math that accompanies the explanation. thanks
  39. J

    Geosynchronous vs geo-stable orbit?

    simple question - can someone please clarify the difference between these two orbits? i recall arthur c clarke's original concept for communication satellites in what i believe he called geosynchronous orbit such that the satellite(s) would remain over a single fixed point on Earth's surface...
  40. A

    Sedna's Long Orbit: Uncovering the Reasons Behind Its Unusual Path

    What does most evidence point to regarding the reasons for Sedna's looong orbit? I think it highly unlikely that the Sun's gravitation can keep it in place.
  41. N

    If there is a satellite in geosynchronous orbit

    Homework Statement Does the centripetal force equal the gravitational force? Homework Equations Fg = G(m1)(m2) / r^2 Fc = 4(pi^2)(m)(r) / T^2 The Attempt at a Solution I have the mass of a satellite in geosynchronous Earth orbit. The period of Earth's orbit, and the Earth's radius and...
  42. D

    Max # of electrons in an orbit

    what is the maximum number of electrons allowed in each of the first 5 orbits of an atomic particle? Is it the same for all elements? or do different ones hove a different maximum numver of electrons possible of being in an orbit?
  43. P

    Energy Bound Orbit: Minimal Radius Calculation

    http://img810.imageshack.us/img810/1883/planet.jpg Uploaded with ImageShack.us Homework Statement I have a body of mass m, which is moving in a circular path around some planet. At a certain instant, the object explodes into two equal bodies. I'm given that the tangential velocity doesn't...
  44. N

    Can a Planet Leave Its Orbit Without External Forces?

    I've got a pretty simple question, and it may sound dumb, but I'm going to ask it anyway: First, I'll preface by saying that from what I understand (and please verify or correct me), planetary orbit in a star system decays over time a la net force. I also have come to understand that the...
  45. L

    Question about falling bodies in orbit and acceleration

    Hello, I’m glad that I found this forum, because there is a question that has been bothering me for some time, and maybe someone on a physics forum like this can set me straight on it. It concerns gravity and acceleration. I understand that when an object such as a space shuttle is...
  46. R

    A proposal to reduce the delta-V to orbit.

    To reach orbit you have to have your vehicle have a horizontal, i.e., tangential, orbital velocity, of about 7,800 m/s and have sufficient altitude, say at least 100 km, the altitude considered to be "space". To get to this altitude you have to have a separate velocity in the vertical direction...
  47. K

    Maintaining Orbit of Two Planets Around Sun: Is it Possible?

    for ease of explanation, imagine that the barycenter of two planets is the center of a wheel and that the planets revolve around the edges of the tire. the center of the tire (barycenter) is in orbit around sun, as if the wheel is rolling around in its orbit. my question is, is this possible? of...
  48. M

    Periodic orbit of Hamiltonian dynamical system in R^2 is stable

    Homework Statement We are given a Hamiltonian dynamical system with a smooth Hamiltonian H:\mathbb{R}^2\to\mathbb{R} on \mathbb{R}^2, with canonical symplectic structure. Suppose this Hamiltonian has a periodic orbit H^{-1}(h_0). Prove that there exists an \epsilon>0 such that for all h\in...
  49. R

    Where did the moon get its orbiting energy?

    For the moon to stay in orbit and not crash down into Earth, it must have sufficient tangential velocity. I'm wondering where/how it initially got the energy to reach this tangential velocity. Thanks.
  50. 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...
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