A vector is a mathematical construct that has magnitude and direction. The cross product of two vectors is a binary operation in three-dimensional space that results in a third vector that is ...
In the present situation, both Earth and Mars are moving in the same direction around the Sun, but the slower one, Mars, appears to move backwards compared to the faster one, Earth. Just an illusion. The retrograde motion of Mars â like the apparent motion of the slower car on the highway â is nothing more than an illusion.
What does it mean for Mercury to be in retrograde? Answer: Retrograde motion is an APPARENT change in the movement of the planet through the sky. It is not REAL in that the planet does not physically start moving backwards in its orbit. It just appears to do so because of the relative positions of the planet and Earth and how they are moving around the Sun. Normally, the planets move west-to-east through the stars at night. This is referred to as prograde motion.