Greatest Elongation

5.8 - Understand the terms:
c) elongation

An inferior planet cannot be seen in opposition so the best position to view it is when it is at a position forming 90° between the Sun and Earth.

The remaining angle is the angle of elongation (e).

Elongation is the angle at which we see an inferior planet, which means that Venus never moves 47° away from the Sun. Mercury has a a maximum elongation of 22°.

The maximum angle of elongation to eastern and western points are called the Greatest Eastern Elongation and Greatest Western Elongation.


Mix & Match
  • Explain the term elongation
  • Explain why we see inferior planets best at the maximum angle of elongation

Thinkquest Elongation