Calculating Velocity & Axes of Planetary Orbits

In summary, the individual is seeking equations for determining the velocity of an entity orbiting another and the two axis of a planetary system. They plan on creating a rudimentary PHP program for a planetary system and are looking for advice on integrating physical laws. They also mention wanting to generate stable systems and are interested in both simulating systems over time and modeling them statically using principles of orbital mechanics. They are recommended a resource for further information.
  • #1
smize
78
1
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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  • #3
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.
 
  • #4
Thank you very much! This will help a lot!
 
  • #5
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?
 
  • #6
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.
 
  • #7
Do you have advice on what physical laws I should integrate into my system?
 
  • #8
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.
 
  • #9
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>. [Broken] It is well written and has some nice chapters on what you are looking for.
 
Last edited by a moderator:

1. What is velocity in the context of planetary orbits?

Velocity is the rate at which a planet moves in its orbit around a central object, such as a star. It is typically measured in kilometers per second (km/s) or meters per second (m/s).

2. How is velocity calculated for a planet in orbit?

Velocity can be calculated using the formula v = √(GM/r), where G is the gravitational constant, M is the mass of the central object, and r is the distance between the planet and the central object. This formula is derived from Newton's law of gravitation and Kepler's third law.

3. What are axes of planetary orbits?

Axes of planetary orbits refer to the two imaginary lines that pass through the center of a planet's elliptical orbit and intersect at the focus point. The semi-major axis is the distance from the center to the farthest point on the orbit, while the semi-minor axis is the distance from the center to the closest point on the orbit.

4. How are the axes of a planetary orbit determined?

The axes of a planetary orbit can be determined by measuring the distance between the planet and its central object at two points in the orbit, known as the aphelion (farthest point) and perihelion (closest point). The semi-major axis is half of the sum of these two distances, while the semi-minor axis is half of the difference between them.

5. Why is calculating velocity and axes of planetary orbits important?

Calculating velocity and axes of planetary orbits allows scientists to better understand the motion and behavior of planets in our solar system and beyond. This information can be used to make predictions about future positions and movements of planets, as well as to study the effects of gravity and other forces on orbital motion.

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