text: The point of closest approach ( the point at which two bodies are the closest ) is called the periapsis or pericentre , from Greek , peri , around , and Î Î Î 1\/2 Ï Ï Î Î 1\/2 . The point of farthest excursion is called the apoapsis ( , apÃ , `` from '' , apocentre or apapsis ( from , ap - , before an unaspirated , or , aph - , before an aspirated vowel , respectively ) ) , ( the latter term , although etymologically more correct , is much less used ) .
simplified: The point of closest approach is called the periapsis or pericentre and the point of farthest excursion is called the apoapsis ( Greek Î Ï Ï , from , which becomes Î Ï before a vowel , and Î Ï before rough breathing ) , apocentre or apapsis ( the latter term , although etymologically more correct , is much less used ) .