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.
When we pass Jupiter or Mars or Saturn, for example, these more outward planets in orbit â which move more slowly than Earth in orbit â appear to reverse course in our sky for a couple of months. A schematic of how retrograde motion works when Earth (T) passes an outer planet (P) as they both orbit the sun (S). The changing viewing angle from Earth makes the projection of the planet against the celestial sphere (A) move backwards (A2-A4) as we pass the slower planet. Credit: Wikipedia user Rursus.