how do scientists measure the ellipticity of a planet's orbit?

Question

what's their method of measurement or calculation?

Answer 1

As far as I know, all you really need is the planet's direction and speed relative to the star it's orbiting, and a few mathematical calculations will then give you the ellipticity to a sufficient degree of accuracy. Any given speed and direction can only be equivalent with one possible orbit, because otherwise the planet could take any of more than one course for literally no reason at all, and logic forbids that.

That said, I don't know precisely what functions you would use in order to determine ellipticity, although if I worked on it for a while I might be able to come up with one.

Answer 2

Once you know a planet's position and motion relative to the sun, it's orbital parameters can be calculated.

Also, the term used to indicate how elliptical an orbit is is eccentricity. An eccentricity of 0 is a circle. An eccentricity of 1 is a parabola and therefore no longer a closed orbit (greater than 1 is hyperbolic). Elliptical orbits therefore have an eccentricity less than 1.

Answer 3

The actual term for this is eccentricity.

A highly eccentric orbit is highly elliptical, and an orbit with no eccentricity is a circle.

Eccentricity is the ratio of the distance between the center of the ellipse and one of its focii, and the ellipse's major axis. That is, divide the distance between the star and the center of the orbit by the nearest distance the planet approaches to the star.

Answer 4

There are various methods of calculating orbits, all of them fairly involved mathematically. The basis of all of them is fitting the solution to Kepler's Laws, which require show the relationship between orbital distance and velocity.

Answer 5

check this http://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion