Transit
every reader
What the tradition reads
A transit is the position of a planet in the sky today, read against the fixed positions of a birth chart rather than against itself, so that a transiting planet's sign, house and aspects to the natal planets are all judged in relation to a nativity that never moves while the transiting sky continually does. Because the transiting planet is genuinely, physically where the chart says it is, unlike a progressed or directed position, which is symbolic rather than actual, the tradition treats transits as the most literal of the timing techniques, and generally allows a narrower orb for them than for aspects within the birth chart itself, since a transit's exactness is understood to matter more precisely to when its effect is felt. Modern astrology reads a transit as opening a period in which the natal potential a chart already shows is given some opportunity to develop or to be tested, rather than as imposing an outcome from outside; a difficult transit is read as pressure toward change rather than as a fixed sentence, and the same transit is read differently depending on what it finds already present in the birth chart it crosses.
The story
Comparing today's sky against a fixed nativity is among the oldest habits of horoscopic astrology, since the same aspect doctrine that reads two planets against each other within one chart applies without any real modification once one of the two positions is simply the sky as it stands on the day of judgement rather than a second natal planet. The specific English word transit is a Latin derived label, descending from transire, to go across or to pass over, the same root that gives English its ordinary sense of a transit as any passage from one place to another, whether a train transiting a station or a planet transiting the face of the Sun. The word carries no reference to astrology in itself; it names an ordinary crossing or passing, and astrology's use of it for the ongoing comparison of today's sky against a birth chart is simply that general sense applied to one particular kind of passage, the sky's own continuous movement across the fixed points of a nativity that itself never moves again once it has been cast.
Written from
Corpus key glossary:transit.