Astronomy.
Celestial Mechanics. Or Astronomy
The "apparent" reverse or backwards motion of a planet as observed from Earth. The innermost planets appear to have a retrograde motion when viewed from Earth.
The earth never reverses direction, nor does any other planet. The APPARENT reversal of direction of some other planets, as seen from earth, is called retrograde motion.
Earth
Earth and Mars, along with Mercury and Venus, are rocky planets.
The planets don't have to "do anything" to "go into" retrograde motion. The retrograde motion, the "moving backward" that planets do as we watch them cross the night sky over the weeks, is due to the nature of the orbit of a planet and to our view of that orbit from earth.
Geocentric motion of planet is that in which earth is at the centre of the universe and all other planets revolving around it.Heliocentric motion of planets is that in which sun is the of universe and other planets revolving around it.In planetary motion all the planets includes Earth revolving around the Sun in their fixed orbit.
The pattern by which planets appear to move backward in the sky relative to the stars is called "retrograde motion." This phenomenon occurs when Earth, on its orbit, passes by another planet, causing the other planet to appear to reverse its usual direction of motion against the background stars. Retrograde motion is an optical illusion resulting from the relative positions and movements of the planets in their orbits.
All planets other than Earth could be considered alien. Earth is the only planet known to harbor life.
The non-gaseous planets, called Rocky planets are Mercury, Venues, Earth and Mars.
The world is a planet called Earth. In our solar system of eight planets Earth is the fifth largest.
in a heliocentric system earth and the other planets revolving planet's a geocentric system ,earth is at the center of the revolving planets