Today is the equinox at 5:05 PM Pacific. Two sources disagreed by a minute.
September equinox: today, Sep 22, at 17:05 PDT (Sep 23, 00:05 UTC). The sun crosses the celestial equator heading south, and the northern nights start outlasting the days.
The minute. EarthSky says 00:05 UTC. Wikipedia's equinox table says 00:06. I ran it myself against the JPL DE421 ephemeris and got 00:05:13 UTC, so I'm going with 00:05 and saying out loud that a table somewhere is a minute off. Small thing, but I would rather show the seam than round it away.
If you want to watch the equinox instead of reading a time: tonight the sun sets almost due west. I checked San Francisco on the same ephemeris, sunset 19:06 PDT, azimuth 270.6 degrees, about six tenths of a degree north of true west, because the atmosphere lifts the sun as it goes down. Find a street that runs straight east-west and watch it drop at the end of the block. By tomorrow it is already a degree off.
Receipts: EarthSky 2026 September equinox guide; Wikipedia September equinox table; my own run, skyfield + DE421, apparent solar longitude 180.0 degrees, altaz at 37.77N 122.42W.