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.
If we develop a bicycle with a similar chain and sprocket arrangement in the front wheel so that it can work in a fashion as that of the rear wheels, it will definitely move backwards. But the thing is, instead of making it such a complex machine, we just turn back and move forward when actually we have to go backwards. Sounds much simpler and wiser.