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.

View More On Wikipedia.org
Recent contents Top users
  1. P

    Rocket Equation and Orbit questions?

    Homework Statement #1.) A rocket exhausts fuel with a velocity of 1500 m/s, relative to the rocket. It starts from outer space with fuel comprising 80 per cent of the total mass. When all the fuel has been exhausted the speed is... (Answer was 2400 m/s) Homework Equations Vrel...
  2. J

    Calculating Orbital Radius from Period: Solving for r without Velocity

    Homework Statement If a new planet has a year of 3.44578 Earth years, what is its radius of orbit in meters if Earth's orbital radius is 149,597,870,700 meters? Formula: r = (vt)/(2pi) How can I use this without velocity? All help is appreciated as I'm not sure how to go about this...
  3. U

    Solar System's orbit around galaxy, a concise 3D description?

    Hello, this is my first topic/question, thanks for reading thus far... It is very easy to find explanations about the general path that the solar system takes when it orbits the center of our galaxy, when viewed in 2D from above, a circle around the center some distance away from that center...
  4. V

    Satellites in Orbit: Mass vs Velocity

    Homework Statement You can determine the velocity of a satellite in uniform circular orbit by applying Newton's second law, Newton's law of gravity, and the centripetal acceleration due to gravity. Which of the following is not correct? a) The orbital radius r and the speed v cannot be...
  5. A

    Change orbit from circle to parabola

    1(a) Homework Statement A spaceship travels in a circular orbit around a planet. It applies a sudden thrust and increases its speed by a factor f . If the goal is to change the orbit from a circle to a parabola, what should f be if the thrust points in the tangential direction? 1(b) Is...
  6. J

    Using Kepler's Law to find speed of a comet in orbit

    Comets travel around the sun in elliptical orbits with large eccentricities. If a comet has speed 2.5×104 when at a distance of 2.3×1011 from the center of the sun, what is its speed when at a distance of 5.9×1010 . Using Kepler's Law T2 is proportional to R3 T2/R3 is a constant (C)...
  7. F

    Spin Orbit Coupling leading to topological insulator behaviour

    Hi I am studying how the spin orbit interaction in certain materials can lead to topological insulator effects and realize it has something to do with the effects of the SOC on the band structure of the material (Bi2Se3), possibly due to the inversion of the valence and conduction band but I...
  8. B

    Since the Sun is losing mass, can a planet's orbit change be measured?

    Since the Sun is changing 4M tons of matter into energy every second and that energy eventually makes its way to the surface and is emitted as an outbound sphere of EM radiation, then the planets' orbits would change over time due to the less massive Sun at the solar system's core. It would...
  9. A

    How does an object orbit something

    I am having a very hard time understanding this concept in physics. Why would something orbit an object? Why doesn't it leave the orbit and move straight? Also when a satellite leaves Earth how does it go into orbit? Does it have to be launched at a specific angle.
  10. T

    Universal Gravity Circular Orbit

    Homework Statement What is the radius of a circular orbit about the Earth where the acceleration is 0.1g? Homework Equations g=9.8m/s^2 F=(Gmm)/r^2 Radius of Earth= 6.38x103 km Mass of Earth= 5.98x10^24 m/s The Attempt at a Solution I said 1/(2^x)=1/10 then did log2(10)=x and solved...
  11. W

    Just how dark is Pluto from orbit? How about Saturn?

    Quick question that maybe someone here could answer. I could probably dig up a bunch of math equations and answer it too, but I'm guessing someone here already has a good idea about the answer. Placing the Sun at the center of a sphere whose radius is equal to the distance of the Sun to...
  12. L

    What is the period of a photon in a circular orbit around a black hole?

    Let be a photon in a circular orbit (r=3M). I want to know the period measured by a stationary observer at this radius. Because we are working with a photon we cannot 'talk' about proper time, that's why I don't understand how can I calculate this. If I had a massive particle I could do...
  13. J

    What speed would a satellite have to be placed to make it into orbit?

    Homework Statement Homework Equations F = G(m1m2/r2) The Attempt at a Solution Well the height of Mt. Everest is 8,848 m. And I'm guessing the no atmosphere and not turning on an axis is just to setup the ideal problem. But from there I don't know how to set up the equation so...
  14. L

    Calculating integral of earths orbit but with visual basic.

    Homework Statement Ok for starters, I wasn't entirely sure whether this was supposed to go under physics or comp sci, this is a 'physics' problem I believe but done through visual basic, anyways. So I have a program where the Earth is animated to orbit the sun based on Newtons laws, I need to...
  15. J

    Symmetries and Spin orbit interaction

    I know that the generators of the Poncaire group that are associated with *orbital* angular momentum belong to an infinite dimensional representation, i.e. \begin{equation} L = \frac{\partial}{\partial \theta} \end{equation} Also the spin generators are associated with some finite...
  16. J

    Showing that a near earth orbit is P = C(1 + 3h/2R_E)

    Homework Statement Show that a satellite in low-Earth orbit is approximately P = C(1 + 3h/2R_E) where h is the height of the satellite, C is a constant, and R_E is the radius of the earth) Homework Equations p=C(1+3H/2R_E) p2 = (4∏2)/(GM) * a3. (G - gravitational constant, M - mass of the...
  17. H

    Understanding Keplerian Orbits: Equations and Time Dependence

    Just curious, does anyone know what are the equations for the displacement-time graph of a Keplerian orbit? The horizontal displacement-time graph should be somewhat sinusoidal, the vertical one cosinusoidal, or vice versa.
  18. G

    How to calculate g (geosync 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. These are called geosynchronous orbits. The altitude of a geosynchronous orbit is 3.58e7 m. Homework Equations v=2∏r/T...
  19. J

    What is the comet's maximum speed at its farthest distance from the star?

    A comet orbits a star. At its closest approach (r=4*10^10 km) it has a speed of v=50 km/s. How fast is the comet at its maximum distance (R=10*10^10 km)? Could someone verify my results? F=GMm/r^2=mv^2/r f=GMm/R^2=mV^2/R F/f = R^2/r^2 = Rv^2/rV^2 -> R/r = v^2/V^2 R=2.5r -> 2.5r/r...
  20. Feodalherren

    How Far is the Satellite from Earth?

    Homework Statement A 320kg satellite experiences a gravitational force 800N. What is the radius of the satellite's orbit? Homework Equations G m1m2 / d^2 The Attempt at a Solution I started with 800N = (G(320kg)(5.98(10^24)kg) / d^2 After some algebra and rounding I ended up...
  21. B

    What Are the Steps to Calculate a Hohmann Transfer Orbit to Jupiter?

    Homework Statement You may assume circular planetary orbits. a. Calculate the velocity (relative to Earth) at Earth's orbit of the Hohmann transfer orbit that is tangent to both Earth's orbit and Jupiter's orbit. b. calculate the minimum velocity necessary to launch a spacecraft from...
  22. O

    Orbit of satellite 2nd order ODE using Matlab

    Hi, I am completely stuck on this problem that has been given to us. I must solve a set of 2nd order differential equations using Euler's method. It is for a geosychronous orbit of a satellite, meaning the orbit is circular and the velocity vector is perpendicular to the radius vector...
  23. J

    Can an Asteroid Impact the Moon's Orbit?

    If an asteroid was moving in the opposite direction of the moon, could it slow it down enough when it hit it to cause it to crash into the earth. and vice versa, could it be going the same direction and acceleration it enough to excape the Earth's gravitational pull? If so, about how large would...
  24. R

    Gravitational Waves & Neutron Stars/Black Holes: Observed Velocity Decrease

    2 closely orbiting massive objects are predicted to deserve the fabric of spacetime so much that they will release a ripple of gravitational waves. When geavitational waves are released, they slowly loose velocity energy and spiral into one another. 2 pulsars were discovered orbiting each other...
  25. R

    Einstein's Theory of Relativity: Why Planets Orbit Quicker Near the Sun

    Einstein predicted a slightly quicker orbit for planets very close to the sun that will deviate from Newton’s gravitational laws very slightly. Later observations, as we know, have proved correct and General Relativity holds up. But what is the perceived reason as to why this is? What is the...
  26. R

    Using iteration to orbit dual suns - losing energy

    Using iteration I've got a satellite flying around two gravity sources. (See picture) When using the iteration over a 100 times I see that TE, total energy slowly sinks so I need to make a correction after each iteration to insure that TE is constant. Trouble is I have several...
  27. onomatomanic

    Tidal implications of eccentric planetary orbit

    I'm world-building for a SF-story and need some help figuring out what the ocean tides would look like. My planet orbits a close binary star system; it does not have any satellites itself. The mass of the binary is 5/3 Mo [solar masses]. The orbit is closer than that of Earth and is highly...
  28. M

    What is the orbital period of a satellite in a low-Earth orbit?

    Homework Statement Consider a satellite in a circular, low-Earth orbit; that is, its elevation above the Earth’s surface is h ≪ R⊕. Show that the orbital period P for such a satellite is approximately P=C(1+ 3h/[2R⊕]). Homework Equations P2 = (4pi2)/(GM) * a^3. (G - gravitational...
  29. P

    Total mechanical energy of a point mass in an elliptical orbit

    Hey, I was trying to prove to myself an expression for the total energy, and I got stuck Here is the picture (it's transparent, so I won't embed it here). The problem I seem to be having is when I observe these two points where the speed is in its highest and its lowest. Since in these...
  30. R

    Do scientists know why planets orbit stars on the same dimentional plane?

    Pretty straight forward. The same generally holds true with moons belonging to the same planet. If we don't have concrete reason why this occurs, are their any strong theories?
  31. A

    Parallax during the earth's orbit?

    Hi, Would the difference in the distance between the Earth and the sun when the Earth is in perihelion and when it is in aphelion be considered a parallax? Thanks,
  32. G

    How much charge would the Earth and Sun need to knock the Earth out of orbit

    Homework Statement How much charge would the Earth and Sun need to knock the Earth out of orbit. Then, assuming the distance from one proton to another and the length of one electron to another is 197 pm, find out how large of a block you would need of protium located on Earth and how large...
  33. AGNuke

    Charge moving in elliptical orbit under Coulomb field.

    Under the influence of the coulomb field of charge +Q, a charge −q is moving around it in an elliptical orbit. Find out the correct statement(s). (A) The angular momentum of the charge −q is constant (B) The linear momentum of the charge −q is constant (C) The angular velocity of the charge...
  34. J

    Finding Eccentricity of Orbit Given Masses, Positions, and Velocities

    Homework Statement Find the eccentricity of an orbit given the masses, cartesian position components, and cartesian velocity components for particles 1 and 2. The case is reduced to the xy plane. Homework Equations I am attempting this problem using reduced mass from the center of mass...
  35. B

    How Fast Do Stars Orbit in Different Galaxies?

    1. How fast are stars orbit speed in elliptical galaxies (from and to) 2. How big differences are there typical between Perigalacticon and Apogalacticon in a. elliptical galaxies and b. spiral galaxies?
  36. D

    Comet near the sun whose orbit is?

    A comet near the sun whose orbit is________ would never be near the sun again is called what? My options are elliptical (I know its not this one), circular, hyperbolic, apogee, and following an inverse square law.
  37. B

    How Is Satellite Orbit Speed Calculated with Atmospheric Resistance?

    When a satellite is affected by resistance against orbit motion, for example from thin atmosphere or solar wind, it will as a result of this decelerates - but in that process it will decrease slightly toward the earth, and therefore following accelerate too. How can the new orbit speed be...
  38. 4

    What is the relationship between a comet's velocity and the shape of its orbit?

    Hello. I read from a calculus book (Larson) that shape of comet's orbit is determined by its velocity in following way. Ellipse if v < sqrt(2GM/p) Parabola if v = sqrt(2GM/p) Hyperbola if v > sqrt(2GM/p) where p is the distance between one vertex and one focus of the comet's orbit...
  39. C

    Calculate foci of planetary orbit given known parameters

    Hello everyone. I am trying to calculate the focal points of the ellipse traced by a planet in orbit around a star, given the following known parameters: M_{sun} Mass of the sun r_{planet} Position vector of the planet from the sun m_{planet} Mass of the planet v_{planet} Velocity of the planet...
  40. R

    Are we travelling slower through time due to the Earths orbit?

    Is it that faster we move through space, the slower we move through time? Is it that we're moving slower through time than if the Earth wasn't orbiting anything? And on a wider scale like, the Sun orbiting the centre of our galaxy, and our galaxy moving through space. How would time be...
  41. E

    How delicate is the Earth's Orbit?

    The Earth has at times been struck by very large asteroids but this has not knocked our planet out of it's orbit. Why not? Does the Earth have some method of 'self correction'? Or is it not a very 'fine tuned' system so that a few impacts really won't make any difference? Alternatively have...
  42. A

    JP Aerospace Airship to Orbit project

    I was looking at JP Aerospace's Airship to Orbit project: http://www.jpaerospace.com/atohandout.pdf I was with it until the third phase: What is the mechanism of electric propulsion? Is it simply a propeller? (I was under the assumption that a propeller would be fairly useless at that...
  43. J

    Satellite in orbit - forces involved

    Homework Statement A satellite orbits the Earth once every 120 minutes. The satellite is in a state of free fall. What is meant by the term free fall? How can the height of the satellite stay constant if the satellite is in free fall? [3 marks]Homework Equations none The Attempt at a Solution...
  44. J

    Calculating Historical Positions of the Asteroid Belt's Orbit

    Is it possible to calculate the historical whereabouts of the asteroid belt, as it seems to be moving ever outward due to the radiometer effect? Can it be calculated, for instance, where it was 1,000 years ago? 100,000 years ago? Etc. In particular, I'm curious as to whether the science is...
  45. A

    Is Amateur Rocketry in Orbit Possible?

    Has an amateur rocket ever made it into orbit?
  46. S

    Asteroid orbit determination from observations

    It is said in the literature, I believe, one needs several nights of observations to calculate an orbit for, say,an asteroid. Using celestial mechanics mathematics and methodology, one produces the six orbital elements. It seems to me that most introductory texts on the subject, talk about...
  47. J

    What happens to shrapnel if a hand grenade explodes in solar orbit?

    Hi, folks. I'm new here and came looking for some expert input on this odd question that came up as a friend and I were considering a hypothetical. Suppose a hand grenade were orbiting the sun---say, half way between the orbits of Mars and Jupiter. And to make things easy, suppose that the...
  48. Spinnor

    Changing the orbit of a satellite, minimum rocket burns.

    Suppose we have a satellite in an elliptical orbit around the Earth with the major axis pointed towards some fixed point in the heavens. What is the minimum number of rocket burns so that the major axis is rotated 90 degrees and the final and initial energy are the same. Is the number 2? At...
  49. N

    Cosmological expansion of earth orbit

    I came across the following at Ned Wrights website and wondered [a] What does the boldface statement mean? [b] What is thought about the statement that "Cosmological expansion of the Earth orbit around the sun is negligible but not zero" instead of "its not been determined"...
  50. A

    Integrating the generator lines of an elliptical orbit

    Hi, I am having difficulty understanding the following: \int^{2π}_{0}(x+y)\,dθ = \int^{2π}_{0} 2a\,dθ = \textbf{4}πa where x and y are the generator lines of an elipse, a is the semimajor axis and θ is the angle formed by x and the major axis. I understand that x+y = 2a. However I...
Back
Top