Planet or star?

Some of the brightest "stars" in the evening sky are planets — Venus, Jupiter, Mars, Saturn. They shine by reflecting sunlight, as the Moon does.

An old rule of thumb: stars twinkle, planets mostly do not. A star is so far away it is a single point, and the air bends that point about. A planet is close enough to be a tiny disc, so the air's wobble averages out.

Planets also wander. Over weeks they shift against the background of stars — the word planet comes from the Greek for wanderer.