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## Homework Statement

Halley’s Comet passed perihelion on 9 February 1986. It has a semi-major axis

a = 17.96 AU and eccentricity e = 0.9673. (One astronomical unit (AU) is the distance

between the Earth and the Sun.) Calculate the period of Halley’s Comet and the

approximate date on which you might next see it.

## Homework Equations

Period = T = 2pi(sqrt(a^3/u)

## The Attempt at a Solution

I realize all this information is available over the internet but I need to work it out by hand.

I attempted this question first using the value for 'a' given and the standard gravitational parameter (u) of earth 3.986E14 but realised this is wrong and that halley's comet would have a different value of (u). I assume the equation for the value of (u) of halley's comet will be related to its eccentricity but can't seem to work it out. Any ideas?