The angle between the Sun and planet is called the angle of elongation. The maximum angles of elongation are about 28 degrees for Mercury and 48 degrees for Venus. So these planets are never seen very far from the Sun. Usually planets move eastward through the Zodiac, but from time to time they change their direction of motion and move westward. This westward motion is known as retrograde motion .
Inferior planets retrograde near inferior conjunction.
At opposition , the phase of a superior planet such as Mars is full. It is on the opposite side of the Earth from the Sun. This means that wherever the Sun is in the sky, the planet will be 180 degrees away. For example, if the Sun is setting, the planet will be rising. A superior planet retrogrades when it is near opposition.