What is a transit in astrology?

Your birth chart is a photograph of the sky at the exact moment you were born, and it never changes. The Sun stays wherever it sat that morning, your Moon keeps the degree it held, every planet frozen where the clock caught it. That fixed map is you.

The real planets kept going, though. Right now, tonight, they are somewhere overhead in live positions. A transit is what happens when one of those moving planets reaches a spot that matters in your fixed chart. Picture two wheels stacked up: your birth chart underneath, the current sky on top. The chart underneath is permanent, while the sky above it has moved every single day since you were born. Where a moving planet lands on one of your natal points, that contact is the transit.

The contact is not vague. A transit counts when the moving planet makes an aspect, a specific angle, to one of your natal points. Sitting right on top of it is a conjunction. A quarter turn away is a square, which reads as friction. A third of the circle is a trine, which reads as ease. Directly across is an opposition, which reads as a tug of war.

So every transit has two names built in: which planet is moving, and which of your points it is touching, at what angle. Transiting Jupiter crossing your natal Sun tends to feel like a door opening, a season where things expand and yes comes more easily. Transiting Saturn squaring your natal Moon tends to feel like weight, a stretch where your feelings ask to be taken seriously. Transiting Venus gliding over your natal Venus is smaller and sweeter, a short lift in your love life or your mood. Same mechanic, very different results.

Here is the part that makes transits matter: they answer when. Your natal chart describes what you are working with, and your Mars sign never changes. Transits say when a given theme is switched on, turned up, or finally easing off. When an astrologer calls a week heavy or a month a turning point, they are reading which planets are currently hitting your chart and how hard.

Speed decides how long a theme lingers. The Moon moves fast, so its transits are done in hours, which is why a mood can lift by dinner. The slow outer planets can sit on one sensitive degree for a year or more, and those are the transits that line up with the chapters you name later.

• Moon: a transit lasts hours. A passing mood, gone by tomorrow.
• Sun, Mercury, Venus, Mars: days to a couple of weeks. Short, specific stretches.
• Jupiter: about a year in each sign. A broad season of growth or luck.
• Saturn: roughly two and a half years per sign. Real structure, real tests.
• Uranus, Neptune, Pluto: years on one theme. The slow, defining chapters.

You have met transits already, just without the vocabulary. Your Saturn Return, around age twenty-nine and again in your late fifties, is simply transiting Saturn coming back to the exact spot it held when you were born. It reliably lands as the stretch where you are pushed to grow up and steady your life. A Jupiter return, roughly every twelve years, is the same idea with a lighter hand.

Mercury retrograde is a transit too, just a famous one. So is the daily horoscope you already read: a Sun sign forecast is a stripped-down transit report, reading where the current planets fall for everyone born under a single sign. A reading built on your whole chart can see which of your exact placements a planet is really touching, which is where transits get personal.