In astronomy, "backward" or "retrograde" refers to the apparent motion of a planet moving in the opposite direction to the stars. This phenomenon occurs when Earth passes by another planet in its orbit, making it seem as though the other planet is moving backward in the sky. Retrograde motion is an optical illusion caused by the relative positions and speeds of the planets. In astrology, retrograde periods are often associated with challenges or disruptions in the areas of life ruled by the retrograde planet. For example, when Mercury is in retrograde, it is commonly believed to affect communication and technology, leading to misunderstandings and technical issues.