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

It comes around ever 75 years, 2061 or so. 

Some sources say July 28, 2061.

We can also calculate it by Kepler's Third Law:

Kepler's 3rd law is a mathematical formula. It means that if you know the period of a planet's orbit (P = how long it takes the planet to go around the Sun), then you can determine that planet's distance from the Sun (a = the semimajor axis of the planet's orbit).

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