What is a transit in astrology?

The sky now on top of the sky then

Your birth chart is frozen at one minute. The planets kept moving. A transit is any contact between where a planet is now and a point in the birth chart: a conjunction, square, opposition or other aspect. If you were born with the Sun at 2° Taurus, any planet passing 2° Taurus makes a conjunction transit to your Sun. ¹

The slow planets matter most to astrologers because they linger. Jupiter spends about a year in each sign, Saturn about two and a half, Pluto anything up to thirty. The fast ones, the Moon especially, pass in hours and are read as moods of a day. ^2,3

How transits are used

Conjunctions and oppositions are traditionally the strongest transits. Astrologers watch for the outer planets crossing the angles of a chart or the Sun and Moon, and treat those as the big seasons of a life. ¹

Newspaper horoscopes are a simplified form of transit astrology: they look at where the planets are this week relative to each sun sign, counting the sun sign as the first house. Astrologers call these solar houses.

Transits and the other clocks

Transits are only one of the timing methods astrologers use. Ptolemy's own was primary directions, which turn the whole chart with the daily rotation of the sky and convert degrees into years of life; the method mattered so much that Placidus designed his house system partly as an aid to calculating it. ⁴

Secondary progressions, a later technique, count each day after birth as a year of life, so the chart for the thirtieth day after you were born stands for your thirtieth year. Solar arc directions move every point in the chart forward by the distance the progressed Sun has travelled. Return charts, drawn when a planet comes back to its birth position, are a special case of transits. ⁵

What sets transits apart is that they are real: the planet really is at that degree in the sky that week, and anyone with an ephemeris can check. Progressions and directions are symbolic clocks.