Halley's Comet has an extremely elliptical orbit around the Sun, with an eccentricity of 0.967. Its average orbital radius is 17.8 AU, and it was last observed in 1986. Use Kepler’s Third Law to calculate when Halley's Comet will appear next. (Note: The answer you obtain is based on averaged data and is an approximation.)
2061
2073
2088
2095

Question

Halley's Comet has an extremely elliptical orbit around the Sun, with an eccentricity of 0.967. Its average orbital radius is 17.8 AU, and it was last observed in 1986. Use Kepler’s Third Law to calculate when Halley's Comet will appear next.  (Note: The answer you obtain is based on averaged data and is an approximation.)
2061
2073
2088
2095

anonymous · Answer

I hope you remember the derivation of the 3rd law of kepler(Generally we only remember the proportionality of the equation)
this is the 3rd law of kepler
$$P^2 = 4\pi^2a^3/GM$$

anonymous · Answer

here a is the average orbital radius 
i cant see the use of e here