Trajectories of planets using reduced mass and CM frame

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SUMMARY

The discussion centers on the application of reduced mass (\u03bc) in analyzing planetary motion within different reference frames, specifically the center of mass (CM) frame and the frame of the star (M). It is established that the trajectory of a planet (m) appears as a conic section when viewed from the star's frame, while in the CM frame, both the planet and the star follow conic trajectories with the focus at the CM. The trajectories remain conic in both frames, but their perspectives differ, leading to distinct interpretations of the motion.

PREREQUISITES
  • Understanding of reduced mass (\u03bc) in classical mechanics
  • Familiarity with conic sections and their properties
  • Knowledge of inertial and non-inertial reference frames
  • Basic principles of celestial mechanics
NEXT STEPS
  • Study the implications of reduced mass in orbital mechanics
  • Explore the mathematical derivation of conic sections in planetary motion
  • Learn about the dynamics of the two-body problem in celestial mechanics
  • Examine detailed plots of orbits transitioning between reference frames
USEFUL FOR

Astronomy students, physicists, and anyone interested in understanding the dynamics of planetary motion and the effects of different reference frames on orbital trajectories.

Soren4
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In planetary motion, the reduced mass of a system \mu is used in order to study the motion of the planet m in the non-inertial frame of the star M. Using \mu the trajectory of m turns out to be a conic. But this is the trajectory of the planet m as seen from the star M, correct?

I read that in the CM frame the trajectories are still conics (ellipses for istance) but that the focus is in the CM. Moreover the Sun (or the star) also follows a conic trajectory with focus in the CM of the system.

Is the trajectory of the planet seen in CM frame different from the one calculated using \mu (and so the one in the M frame)?
 
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Soren4 said:
In planetary motion, the reduced mass of a system μμ\mu is used in order to study the motion of the planet mmm in the non-inertial frame of the star MMM. Using μμ\mu the trajectory of mmm turns out to be a conic. But this is the trajectory of the planet mmm as seen from the star MMM, correct?

I read that in the CM frame the trajectories are still conics (ellipses for istance) but that the focus is in the CM. Moreover the Sun (or the star) also follows a conic trajectory with focus in the CM of the system.

Is the trajectory of the planet seen in CM frame different from the one calculated using μμ\mu (and so the one in the MMM frame)?

if you see the resources on the net detail plots are there of the orbits when the observer moves from centre of mass frame to one of the bodies.

for example
[PDF]The Two-Body Problem - KSU Math Home
https://www.math.ksu.edu/~dbski/writings/twobody.pdf
 

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