Why planets are subjected to retrogression? What are the main reasons for retrogression? These are few very important questions that any astrology student would like to know. All planets circle around Sun. To say, Sun is a planet it will be more apt to say Sun is a star. Sun throws gigantic fiery rays, it is beyond our imagination to even think about the energy of all the other stars especially the 27 nakshatras. All these stars (including Sun and Nakshatra) create huge system of gravitational pull and push through fiery rays.
As such all the planets from Pluto to Mercury circle round the Sun, a baby star. All these planets travel along the path of the 27 nakshatra/stars and does not circle around the 27 stars. Planets do not have the strength to do so. If they have the strength to do so, all these planets including Sun will be reduced to ashes with the heat of their own energy.
As the planets go round the Sun, the three outer planets in Vedic Astrology namely Mars-Satum-Jupiter, as they reach roughly 150° towards Sun, Sun by its mighty and fiery magnetic rays alter their transits to an apparent backward motion, commonly known as Retrograde motion. In the same manner, the Retrograde planets from the Sun positron, moving at 270° becomes direct and moves forward. That is planets from Sun in the 9th house becomes retrograde and from Sun in the 5th house gets direct.
Similarly, the Inner planets Venus and Mercury also get retrograde, but with a difference, compared to the Outer planets Mars-Saturn-Jupiter. The Outer planets Mars-Saturn-Jupiter gets retrograde as they move towards Sun. In the case of Mercury and Venus they get into retrograde motion as they move away from the Sun. They are always supposed to be closer to the Sun. That is Mercury and Venus are never allowed to cross 3rd house from the Sun. It is the magnetic pull from the Sun does not allow these two inner planets to move away.
For this reason, Sun from its position allows Mercury to reach 20° to 21°, and beyond that gets Mercury to retrograde to hold itself within the three houses lomit. As and when Mercury
transiting behind the Sun, the same cosmic order will be followed. For Venus, it is to become retrograde roughly at 28° flom Sun. As and when Venus trails behind the Sun. retrogression will be In
the same order. That is Mercury and Venus while transiting from Sun behind to it or ahead of it should not cross the third house. Of all the planets it is the Mercury that gets ret retrograde
very often, as it is closer to the Sun.