While the astronomical spring equinox (usually falling around September 22nd or 23rd) marks the technical start of the season in many countries, Australia has widely adopted the "meteorological" start date of the 1st of the month for simplicity and record-keeping.
As a season of transition, spring is widely considered one of the best times to visit "Down Under" due to mild temperatures, blooming wildflowers, and lower travel costs before the summer rush. Seasonal Overview & Weather by Region when is spring in australia