8

A Comprehensive View

place; it is said to be in opposition, whenthe earth is between the fun and planet.

The elongation of a planet

19. Is its apparent distance from the fun,

; as seen from the earth. A planet has noelongation when in conjunction with thefun ; in opposition, it has 180 degrees. Infig. 5. tTt represents a part of the earth’sorbit; T the earth, S the fun; ACE anarch of the starry sphere, and d the placeof Venus in her orbit. A spectator uponthe earth at T would refer the fun’s placeto those fixed stars at C, and that of Venusto those at D : in this cafe the angle C T Dis the apparent distance between the fun andVenus, and is called the angle of elonga-tion.

zo. An inferior planet may be in con-junction with the fun in two situations;1. when it is between the earth and thefun, called the inferior conjunction ; 2. whenthe fun is between the earth and planet,called its superior conjunction ; but it cannever be in opposition to the sun.

21. The greatest elongation of an inferiorplanet is when a line T E, drawn from the

earth