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Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or nutation of an object's rotational axis .
Apparent retrograde motion of Mars in 2003 as seen from Earth The term retrograde is from the Latin word retrogradus – "backward-step", the affix retro- meaning "backwards" and gradus "step". Retrograde is most commonly an adjective used to describe the path of a planet as it travels through the night sky, with respect to the zodiac , stars ...
The Sun-centered positions displayed a cyclical motion with respect to time but without retrograde loops in the case of the outer planets. [dubious – discuss] In principle, the heliocentric motion was simpler but with new subtleties due to the yet-to-be-discovered elliptical shape of the orbits. Another complication was caused by a problem ...
A satellite with an orbital inclination between 90° and 180° (or, equivalently, between 0° and −90°) is said to be in a retrograde orbit. [note 2] A satellite in a direct orbit with an orbital period less than one day will tend to move from west to east along its ground track. This is called "apparent direct" motion.
In addition, Copernicus's theory provided a strikingly simple explanation for the apparent retrograde motions of the planets—namely as parallactic displacements resulting from the Earth's motion around the Sun—an important consideration in Johannes Kepler's conviction that the theory was substantially correct. [53]
Planets moving in direct motion, aka non-retrograde planets, act in a very predictable way without much fuss or fanfare. Most of the time, planets move in this forward motion, and things carry on ...
English: An astronomical explanation for Mercury's retrograde motion: the inner planet appears to retrace its steps a few times per year. Every planet does this, every year. In fact, there is a planet in retrograde for 75% of 2020.
Mercury retrograde is an astrological phenomenon where the planet Mercury appears to move backward in its orbit from Earth’s perspective. ... when Mercury goes into retrograde motion, any of ...