When I first published this blog entry I wrote that the first day of autumn happens on the 23rd because I did a search on google and found the Calendar Date website that says the first day is on the 23rd. My mother's calendar even says it starts on the 23rd!! The Holiday Smart website, which is apparently based in Florida, also says it starts on the 23rd. Just goes to show that you should be careful about trusting anything you read.
According to the US government's website (my mom asked can we trust them?) the first day of autumn is on the 22nd of September. It explains it like this:
The autumnal equinox marks the first day of the fall season. On this day, the Sun is again directly over the earth's equator, and daylight lasts 12 hours in the Northern Hemisphere and decreasing. This day is typically recognized as September 22 in the Northern Hemisphere. In the Southern Hemisphere, the first day of spring is recognized on September 23.
It lists the first day of autumn as being on the 22nd and says that the autumnal equinox starts this year, 2010, at 11:09 p.m. ET, so that would be 8:09 Pacific Time. And of course you don't have to take the government's word for it--Timeanddate.com says that the "September equinox occurs at 03:09 (or 3:09am) Coordinated Universal Time (UTC) on September 23, 2010." It also has a page where you can find out when it starts in the time zone where you live and a page that explains September equinox in helpful detail.
Since autumn starts so late at night, our family is going to enjoy our last day of summer tomorrow and celebrate the arrival of autumn on the 23rd. Whatever day you choose, I hope you have a wonderful next couple of days enjoying the beginning of the new season!