1. The problem statement, all variables and given/known data Consider Comet Halley. At a particular instant in time, its position and velocity are given below, in units of AU and AU/yr relative to the centre of the Sun. (x,y,z) = 0.331060, -0.455488, 0.166180) (vx,vy,vz) = (-9.01154, -7.02645, -1.30645) There are a number of questions attatched to this problem, all of which are dependent on the answer of part a, which is all I need. a) What are the semi-major axis and eccentricity of this comet? 2. Relevant equations [tex]\alpha[/tex]/r = 1 + [tex]\epsilon[/tex]cos[tex]\theta[/tex] where [tex]\alpha[/tex] = l2/[tex]\mu[/tex]k and [tex]\epsilon[/tex] = sqrt(1 +2El^2/mu k^2) 3. The attempt at a solution We've done a similar problem in two dimensions, given two components of speed, finding E, l and alpha, but in this case I'm not sure where to start. Also, mass is not given so condensed mass mu cannot be found. Maybe an assumption since m << Mass of the Sun? Should I find the radius by sqrt(x2+y2+z2)? If I do, I'm left with 3 components of speed that I don't know how to start working with. I'm stuck and think I just need a push, any help would be great thanks.