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The retrograde motion of a hypothetical extremely distant (and nearly non-moving) planet would take place during a half-year, with the planet's apparent yearly motion being reduced to a parallax ellipse. The center of the retrograde motion occurs at the planet's opposition which is when the planet is exactly opposite the Sun.
The instant of opposition is defined as that when the apparent geocentric celestial longitude of the body differs by 180° from the apparent geocentric longitude of the Sun. [1] At that time, a body is: in apparent retrograde motion [2] visible almost all night – rising around sunset, culminating around midnight, and setting around sunrise [3]
At perihelion, Mercury's orbital angular velocity slightly exceeds the rotational velocity, making the Sun appear to go retrograde. Four days after perihelion, the Sun's normal apparent motion resumes. From the moment the top of the Sun can be seen to the moment someone can see a full circle, a sunrise would take almost 6 hours. [2]
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 ...
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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 .
The Mercury retrograde phenomenon is associated with misfortune by some - but does it really affect us?
This is called "apparent direct" motion. A satellite in a direct orbit with an orbital period greater than one day will tend to move from east to west along its ground track, in what is called "apparent retrograde" motion. This effect occurs because the satellite orbits more slowly than the speed at which the Earth rotates beneath it.