Very basic
Sometimes very basic astrology questions can be answered outside of the "Astrological World." In grade school we learned that the Earth revolves around the Sun in 365.25 days. Since the Earth travels an eliptical orbit and Earth's axis tilts in a constant amount (about 23 degrees) we have a seasonal phenomena wherein we enjoy summer in the northern hemisphere during the months of May thru September -- the souther hemisphere has summer from November thru March. Due to these repeating cycles of Winter, Spring, Summer and Fall, people all over the world adopted this annual cycle as the basis for their calendar. While some groups had differing numbers of "months" or sub-divisions, they all had 365 days or so in their annual calendar. This is not "astrological" as such, it is just basic life and cultural development.
While other planets also have cycles, their cycles are calculated relative to their revolving around the Sun and we do not "see" the weather on those planets. Nor do their cycles directly affect our seasonal cycles. Our own planet revolves around the Sun and has its seasonal cycle which we experience on a day to day basis.
Our movement around the Sun is quite regular in motion, one day or earth revolution does not vary from another expect for small amounts. Because we are on the Earth and the motion is regular and quite constant, the Sun always appears to advance through the zodiac almost one full degree per day. On the other hand, from our position on earth, the other planets appear to move in a more eccentric manner -- some of them appearing to back up or "retrograde" in their apparent (relative) motion for a third of a year, some less. The outer planets appear to retrograde when they are opposite the Sun relative to our position on Earth. The inner planets, of course, only appear to retrograde when they are close to the Sun -- and then only when between the Earth and the Sun. On the far side of the Sun they are moving faster than Earth and appear to be moving faster than the Sun's daily advance.
Because we measure planetary position and movement against the zodiac by sign and degree, the retrograde motion of the planets can easily be seen and calculated. A great deal of literature has been generated relative to when a planet goes retrograde, becomes apparently stationary, and the advances past its original point of retrogradation. When these three points are at/near personal points in ones chart, astrologers pay attention to these times and offer views as to how the person will be impacted. This is a fascinating area of study. The three points appear to quite important many times, but not all of the time, as they trigger planets and aspects in a natal chart. Dave