Today officially the autumnal equinox. It mean the centre of sun is at same plane as the Earth's equator.
The term equinox is derived from two Latin words, aequus (equal) and nox (night). From the word its mean the day and night is equally long, which actually no very true. The day when the day and night is equally long is called equilux, which actually very near to equinox.
Equinox usually occur around 22/23 September, however it may happen on 24th September. It occurred once in year 1931 and it will occur again in year 2303. So most of us will miss both of the occurrence.
Apart of that what equinox mean?
For Chinese, autumnal equinox usually happen around Mid-Autumn festival, which is yesterday. But due to the lunar calendar is using slightly different calculation, therefore Mid-Autumn festival will usually celebrate between mid September and early October. But some of the countries define autumnal equinox as the beginning of autumn.
Anyway, for me, it mean I have about 3 months before the new year is reached. Autumn always consider as the harvesting season and keep the food for the coming winter. I should start doing that also.