Calculating Velocity & Axes of Planetary Orbits

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Discussion Overview

The discussion revolves around the calculations and concepts related to planetary orbits, specifically focusing on determining the velocity of orbiting entities and the characteristics of their axes. Participants explore the theoretical and practical aspects of simulating planetary systems using programming.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks equations for calculating the velocity of an orbiting body and the major and minor axes of its orbit.
  • Another suggests looking at online resources for the necessary equations and algorithms for orbital simulation.
  • Some participants propose that the major and minor axes may not be necessary for the intended simulation.
  • A participant expresses a need for a coordinate system to determine the specific location of a planet over time, mentioning the importance of eccentricity or semi-minor axis.
  • There is a discussion about the emergent properties of orbits in a multi-planet system, indicating that they may not form perfect ellipses due to gravitational perturbations.
  • Participants discuss the physical laws to integrate into the simulation, focusing on mass, distance, force of attraction, and initial velocity.
  • One participant clarifies their interest in generating static examples of stable systems rather than simulating dynamic systems over time.
  • There is a suggestion that modeling static systems and simulating time-based systems are fundamentally different approaches.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of certain parameters (like major and minor axes) and the approach to simulating versus generating planetary systems. The discussion remains unresolved regarding the best methods for achieving the participant's goals.

Contextual Notes

Some limitations are noted, such as the dependence on specific definitions of orbital mechanics and the complexity of simulating multiple interacting bodies.

Who May Find This Useful

Individuals interested in programming simulations of planetary systems, those studying orbital mechanics, and developers looking to create game engines based on astronomical principles may find this discussion relevant.

smize
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As my state (Indiana) has removed Astronomy from the curriculum, my school no longer offers it. I have taken AP Physics B and that is my best knowledge provided by the modern school system, so I apologize ahead of time for any low-level or simple questions.

I am wanting to know the equations for determining:

1. The velocity of an entity orbiting another (i.e. a planet around a star)
2. The two axis (major and minor)

I'm wanting to build a rudimentary PHP program for creating a basic planetary system, so this will help me become one step closer, thank you!
 
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And you might want to look up orbital simulator algorithms to see some of the better - and poorer - ways of writing it. For example, you likely won't need major and minor axes.
 
Thank you very much! This will help a lot!
 
DaveC426913 said:
And you might want to look up orbital simulator algorithms to see some of the better - and poorer - ways of writing it. For example, you likely won't need major and minor axes.


I will be wanting to create a coordinate system where you can tell the specific location of the planet at a given time, which I would denote p(t). I would need to know either the eccentricity or semi-minor axis. Is there any pattern to semi-minor axes/eccentricity of planets?
 
smize said:
I will be wanting to create a coordinate system where you can tell the specific location of the planet at a given time, which I would denote p(t). I would need to know either the eccentricity or semi-minor axis. Is there any pattern to semi-minor axes/eccentricity of planets?

Well, I'll leave it you how you do the simulation. When I programed my simulator, I simply needed distance, mass and force of gravity, updating positions and velocities iteratively. Whether they actually formed ellipses at all was a totally emergent property. And in a star system with more than one planet, you should not be getting ellipses anyway, since they'll perturb each other. That's usually the point of a simulation.
 
Do you have advice on what physical laws I should integrate into my system?
 
smize said:
Do you have advice on what physical laws I should integrate into my system?

Only those three factors. Mass of the bodies, distance between them and force of attraction. Oh, and initial velocity.
 
Alright, thank-you. I really want to create a star system generator someday.
 
  • #10
smize said:
Alright, thank-you. I really want to create a star system generator someday.

Have you seen Universe Sandbox?
 
  • #11
No. What is it programmed with?
 
  • #12
smize said:
No. What is it programmed with?

Nevermind; I have found it. What I'm wanting to do is be able to generate, for example, 1000 systems in a matter of minutes and collect them in a database using PHP. It could be the basis for a game engine for text-based or browser-based games (which are more realistic).
 
  • #13
smize said:
Nevermind; I have found it. What I'm wanting to do is be able to generate, for example, 1000 systems in a matter of minutes and collect them in a database using PHP. It could be the basis for a game engine for text-based or browser-based games (which are more realistic).

Oooooh! You're not interested in simulating systems over time, you're interested in generating static examples of stable systems!

Sorry - I misunderstood.

That's complEEEtly different!

And not something I can help you with.
 
  • #14
DaveC426913 said:
Oooooh! You're not interested in simulating systems over time, you're interested in generating static examples of stable systems!

Sorry - I misunderstood.

That's complEEEtly different!

And not something I can help you with.

Correct. As I get the basics of each system down, I will then make it more complex. (Adding the orbits of systems around a central mass, etc.). What is an example you were thinking of though? I think what I'm going for is the ability to actually do both, but mostly the latter.
 
  • #15
smize said:
Correct. As I get the basics of each system down, I will then make it more complex. (Adding the orbits of systems around a central mass, etc.). What is an example you were thinking of though? I think what I'm going for is the ability to actually do both, but mostly the latter.
Both wouldn't make sense. It'd take millions or billions of orbits to see stable orbits materialize.

You either simulate it in time, or you model it statically using principles of orbital mechanics.
 
  • #16
Alright, I believe I comprehend now. I'm just curious but how do you personally go about the former?
 
  • #17
Try <http://orca.phys.uvic.ca/~tatum/celmechs.html>. It is well written and has some nice chapters on what you are looking for.
 
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