Finding Kelper's Constant with only radius or period given.

In summary, the person is trying to find Kepler's constant for the last four moons of Uranus. They are given the radius and period for the first four, but are not given the mass of Uranus. They are able to find the Kepler's constant by using the radius and period from the first four moons and the T from the last four.
  • #1
zeion
466
1

Homework Statement



I'm given a chart that states the r average and T in Earth days for the moons of Uranus and I have to find the Kepler's constant for the last four moons, which only gives me either the radius or period.. I am confused. How can I find K with only r or T? I need at least the mass of Uranus yes?


The Attempt at a Solution



Am I suppose to find out the mass of Uranus myself somehow?
 
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  • #2
What is Kepler's constant?

Isn't it going to be the same for any orbits of the same body - Uranus in this case?

K = T2/r3
 
  • #3
I'm being asked to find K for each individual moons; each of which has a different period and radius. I was given both the T and r for the first four so I could find K easily, but for the last four I'm only given either r or T, which I think would require me to use

GM/4(pi)^2 = K = r^3 / T^2

But since I wasn't given mass of Uranus (M), I can't :/

The formula IS K = r^3 / T^2 right?
 
  • #4
zeion said:
I'm being asked to find K for each individual moons; each of which has a different period and radius. I was given both the T and r for the first four so I could find K easily, but for the last four I'm only given either r or T, which I think would require me to use

GM/4(pi)^2 = K = r^3 / T^2

But since I wasn't given mass of Uranus (M), I can't :/

The formula IS K = r^3 / T^2 right?

I think the point is that you use Kepler's Constant from the ones you are given to determine the other missing variables for what you aren't given, because it should be after all a constant for objects orbiting the same body right? Kepler's 3rd Law?

http://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion#The_Third_law

T12/r13 = T22/r23
 
  • #5
Oh okay, I think you're right.
Thanks.
 

1. What is Kepler's constant?

Kepler's constant, also known as the third law of planetary motion, is a mathematical relationship between the orbital period and the average distance of a planet from the sun. It states that the square of a planet's orbital period is directly proportional to the cube of its average distance from the sun.

2. Can Kepler's constant be calculated with only the radius or period given?

Yes, Kepler's constant can be calculated with only the radius or period given. However, it requires an additional constant known as the gravitational constant, which relates the gravitational force between two objects to their masses and distance. With this constant, Kepler's constant can be calculated using the formula K = 4π²/G, where G is the gravitational constant.

3. How is Kepler's constant used in astronomy?

Kepler's constant is used to study the motion of celestial bodies, such as planets and moons, in our solar system and beyond. It allows scientists to accurately predict the orbital periods and distances of these objects, and has been instrumental in discovering exoplanets and understanding the dynamics of our solar system.

4. What are the units of measurement for Kepler's constant?

The units of measurement for Kepler's constant depend on the units used for the radius and period. If the radius is measured in meters and the period in seconds, then Kepler's constant will have units of meters cubed per second squared.

5. Are there any limitations to using Kepler's constant?

While Kepler's constant has been proven to be accurate in predicting the motion of celestial bodies, it does have some limitations. It assumes that the orbiting objects are in circular orbits and that there are no other significant gravitational forces acting on them. In reality, orbits can be elliptical and there may be other objects or forces affecting the motion of the orbiting body.

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