Transits are based on the actual movement of the planets in real time.  (whether that time is moved forwards or backwards)  As the planets make aspects to natal planets, certain thrusts usher in events as catalyst for development. Due to the planets from Mars inwards moving so quickly, we normally don’t pay any attention to them, unless we are already looking at a certain timeframe.  Mars circles the horoscope in roughly two years time, so doesn’t point to longer-lasting themes, but is often a shorter-term stimulus for further reaching changes, signified by the outer planet transits.  Transits are the primary astrological activation.  If the Sun is at 11° Cancer at birth and now planet X is at 11° Capricorn, opposing that Sun, planet X will be imparting its (developmental) themes upon whatever my natal Sun means in my horoscope.  (relating to the core me and how I get my appreciation needs met)  When analyzing events, normally an orb that is around 1° 21’ of arc will pull all relevant aspects into consideration.  As there are often three passes of a planet as it aspects natal positions, it is hard to pinpoint the timing of major events relating to the whole circumstance, defined by merely transiting asepccts.  Luckily, we have better and additional tools to help us get a better glimpse into the future and perhaps most importantly, understand WHY what happens needs to be happening… This system works 100% as well in the converse as in direct motion.