What is the Equation for Calculating Halley's Comet Eccentricity?

[orbitsnerd]

Homework Statement

I am given Rp=.6AU and need to find the eccentricity.

Homework Equations

Rp=a(1-e)

The Attempt at a Solution

I can find what Halley's comet eccentricity is (0.967) but I need to actually calculate it. What is the equation I need? I know I need to know Ra, or a, or p.

 

[gabbagabbahey]

Are you told the period of Haley's orbit?

 

[orbitsnerd]

Are you told the period of Haley's orbit?

yes, I guess I was and overlooked it. It was stated in 1910-1986, so 76 years. I can now find a and solve the problem. Thanks!