the stars ??? ??? ??? ellipse an oval ??? ??? ??? astronomical unit (AU) average distane from Earth to the sun; 1.5 X 10 to the 8th power, or 150 million kilometers ??? ??? ??? rotation the spinning of a body, such as Earth, about its axis. ??? ??? ??? revolution the motion of one body about another, as Earth about the sun ??? ??? ??? precession a slow motion of Earth's axis that traces out a cone