What's happening
The Sun's ingress into Aries is the vernal equinox in the northern hemisphere, the autumnal equinox in the south. The Sun crosses the celestial equator moving north, the lengths of day and night pass briefly through parity, and the tropical zodiac restarts at 0° Aries.
Astronomically this is a geometric event. Culturally it is one of the oldest markers of a new year — older than January, older than the Gregorian calendar.
The tradition
Aries is ruled by Mars and is the first of the cardinal signs. Cardinal signs begin seasons; Aries begins the whole cycle. The tradition describes this as pure initiative — the impulse before deliberation, the act of starting without waiting for conditions to be ideal.
Many astrologers still read a chart cast for the exact equinox as an ingress chart for the year, a snapshot of the weather ahead. Whether or not you take that literally, the moment is a reliable cue to notice what is actually beginning and what is only being tidied up.
How to work with it
Treat this as a fresh page with real consequences. Aries is impatient with planning that never ships. Pick the thing that has been waiting for the right time and give it a first move, however small. The point is not to launch everything at once; it is to remember that beginnings are available.
The shadow is heat without direction. Aries without a destination burns through its own fuel and calls that progress. Choose a target before you choose a pace.
The simple rule
Ask what you would do first if you trusted that starting was the work. The Sun in Aries tends to reward the answer you already know.