Ingress

An ingress is the instant a moving point, a planet, or the Sun itself, crosses the boundary between two signs and enters the next one. It happens once per sign per orbit for a fast body like the Moon, roughly monthly, and once a year for the Sun, which is why 'zodiac dates' are really just a list of the Sun's twelve yearly ingresses. Because the crossing is a single instant rather than a stretch, an ingress can be timed precisely, to the second in principle, and this site's dates are given to the minute for exactly that reason. A given year's Solar return, the day the Sun comes back to the exact degree it held at your birth, is its own kind of ingress-like return, tracked the same way: one instant, found and named.