4-22, Freedman and Kaufmann, Universe, 7th ed.) What is the semimajor axis of this orbit? 18. Consider a comet in a long, thin elliptical orbit with a semi-major axis of one AU. What can you say about the sidereal period of this comet? A) It will be less than one year. B) It will be one year. C) It will be more than one year. D) It is not possible to determine the comet”s sidereal period without knowing the eccentricity of its orbit.