Calculating Distance of a Planet from its Sun for Energy Determination

In summary, the conversation discusses the determination of the distance a planet is from its sun for a one-year cycle in order to determine the amount of energy it will receive on any given day. The focus is on finding a general equation to model any planet orbiting any star at any distance, and the use of polar coordinates is suggested for this purpose.
  • #1
Blissfulpain
"Radius" of an Ellipse

a couple things I'm trying to fit together.

First: a planet orbits a sun (positioned at one focus) at an certain speed. At any given time of year it will be at that same spot year after year... i have little clue how to make that work or solve for it.

Second: i need to take that point and deterimine what it's distance is from the sun.

Note: i am a high school graduate, but did only average in mathematics and conics was most certainly not a strong point, however i have a bascic understanding.

Purpose: i need to determine the distance a planet is from it's sun for a 1 year cycle to determine the amount of energy it will receives on any given day.

thx
 
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  • #2


Originally posted by Blissfulpain
First: a planet orbits a sun (positioned at one focus) at an certain speed. At any given time of year it will be at that same spot year after year... i have little clue how to make that work or solve for it.

That only works if your definition of 'year' is the time it takes for the planet to go around the sun once. But that's circular reasoning and not very interesting...


Second: i need to take that point and deterimine what it's distance is from the sun.

You might want to study http://home.cvc.org/science/kepler.htm [Broken]
 
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  • #3
Originally posted by BlissfulPain
First: a planet orbits a sun (positioned at one focus) at an certain speed. At any given time of year it will be at that same spot year after year... i have little clue how to make that work or solve for it.
Make what work? Solve for what? What exactly are you trying to do? Do you know the equation for the ellipse? Do you have it in terms of time?

Originally posted by BlissfulPain
Second: i need to take that point and deterimine what it's distance is from the sun.

If you have the equation for the ellipse in a coordinate system with the sun at the origin it's easy.

Originally posted by BlissfulPain
Purpose: i need to determine the distance a planet is from it's sun for a 1 year cycle to determine the amount of energy it will receives on any given day.

If you know the maximum and minimum distances from the sun to the planet, then you can set it up the equation of the ellipse:
x2/a2+ y2/b2= 1.

You're not completely out of the woods after you have done that. You still need to associate each point with time. You say "at a constant speed". You do understand that planets do not maintain a constant speed as they orbit the sun? (They move faster as the get closer to the sun, slower as they move away.)
 
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  • #4
well, i suppose speed is less relavent... hmm. uh well, ok i'll try to explain.

i want to be able to model any planet orbitting any star at any distance. so i need to be able to have a general equation and have numbers plug into that and then get a nice answer.

first thing i need to figure out is how do i determine the distance the planet is from a star if i know it's major and minor axis.

i sort of re-thought the orbital speed and that's less important, because if i use a cartesian plane then it will move around the star focus at X-degrees per day kinda thing i guess.. and that would stay constant.. so orbital speed is not important really.

i know the quation of an ellipse is (a^2/x^2)+(b^2/y^2)=1 but i don't really understand how to use that or re-arrange it to determine any sort of distance equation (or find a point at a certain time of year or in my case a certain angle in relation to the sun focus).

so i guess what I'm saying is that if the planet is at 180 degrees, then it's on the left side of the major axis (of a horizontal ellipse), and is lined up with both foci. i don't know how to figure out how close the star is though (if the star is the left focus). nor do i know how to determine the distance at any other point in the orbit (or degree compared to the left focus, where the right side of the x-axis would be 0 degrees and the left side would be 180)...

i hope i didn't confuse anyone more.. i just don't have an equation, so there are no specific numbers. if you must, you can use an ellipse with a minpr axis of 3 and a mojor of 4, the star is the left focus of a horizontal ellipse. it would be much appreciated if you could give me any sort of general equation(s) to find the distance the planet is from the sun at anypoint of the ellipse and also determine that point based on any sort or method of a "time of year" scale
 
  • #5
Generally, "orbital mechanics" is done in polar coordinates with the origin at the sun. In polar coordinates the equation of an ellipse (in fact, any conic section) is

r2= a2(1- e2)/(1- e2cos2θ)

where (a,0) is the point where the orbit crosses the positive x-axis (θ= 0) and e is the eccentricity of the orbit.
 
  • #6
ok thx, i'll look up stuff on orbital mechanics... i'll ask if i have more questions. thnks for the help
 
  • #7
i sort of re-thought the orbital speed and that's less important, because if i use a cartesian plane then it will move around the star focus at X-degrees per day kinda thing i guess.. and that would stay constant.. so orbital speed is not important really.

That's incorrect too...
 

What is the radius of an ellipse?

The radius of an ellipse is the distance from the center of the ellipse to any point on its perimeter.

How is the radius of an ellipse calculated?

The formula for calculating the radius of an ellipse is sqrt(a*b), where a and b are the semi-major and semi-minor axes of the ellipse, respectively.

Can the radius of an ellipse be negative?

No, the radius of an ellipse cannot be negative since it is a distance measurement and cannot have a negative value.

Is the radius of an ellipse the same as the diameter?

No, the radius of an ellipse is half the length of the diameter. The diameter is the longest chord of an ellipse that passes through its center.

How does the radius of an ellipse compare to that of a circle?

The radius of an ellipse is similar to the radius of a circle in that it is a distance measurement from the center. However, the radius of a circle is constant, while the radius of an ellipse varies depending on the orientation of the ellipse.

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