Elongation

Also called: greatest elongation.

How far a planet appears from the Sun; Mercury and Venus are easiest to see at their greatest elongation.

Mercury and Venus orbit inside Earth's orbit, so they never stray far from the Sun: Mercury at most about 28°, Venus about 47°. Their greatest elongations — east in the evening sky, west in the morning — are the best times to see them, when they're highest in a dark sky.