Equinox arrives at 5:18 p.m.
The fall, or autumnal equinox arrives this afternoon just as the rush hour begins - at 5:18 p.m. That's the moment when the the sun, as seen from Earth, crosses the planet's equatorial plane 
and heads for the southern hemisphere. And, the sun rises due east today.
Or, you could say the Earth's northern hemisphere is no longer tilted toward the sun, or the length of the night is equal in both the northern and southern hemispheres. You can also note the place on your western horizon where the sun sets, and watch in the coming days and weeks how quickly that spot moves to the south.
It is the official end of summer and the beginning of autumn for the northern hemisphere, and the first day of spring for those south of the equator. So we're off to work today in summer, and return home tonight in the fall.
You can read more about the equinox here.
(NASA illustration)
Comments
This isn't a big deal, but I've always wondered about something. People are fond of saying that a season "officially" starts on the day of a certain equinox or solstice, but what's the source on that? Is there any authority or organization that claims general scope over such things (not just within a particular area, like astronomy or agriculture)?
FR: Nah. It's just a cultural tradition, and such things can change. The Celts believed the seasons began on "cross-quarter days," halfway between the solstices and the equinoxes. So, for example, winter began "officially" for them at Samhain, which occurred around the first of November. The solstice, around Dec. 21, was celebrated as "mid-winter," just as June 21 was once celebrated (still is in Scandanavia) as Midsummer's Night.
Posted by: Mike Klein | September 22, 2009 11:51 AM
i cant whait till 5:18pmmmmmm yahoooooooooo
Posted by: chris | September 22, 2009 1:47 PM
Thank you, Frank!
Posted by: Mike Klein | September 22, 2009 3:21 PM
Frank, the official name for this season is Autumn.
"Fall" is basically slang when used to describe Autumn.
FR: Perhaps with reference to the equinox. But otherwise it's OK in my dictionary, at least in the U.S. And I'll bet you'd get an argument from plenty of readers. Readers?
Posted by: Hazmat77 | September 22, 2009 6:24 PM
Not quite related, but I thought you'd like this storm-hunter comic : http://xkcd.com/640/
Posted by: April | September 23, 2009 7:40 AM
Although I say Fall from time to time, Autumn is such a lovely word for such a beautiful season I think it should be used more often.
FR: If fall were outlawed, what would become of Princess Summerfallwinterspring ? Or am I the only one old enough to remember her?
Posted by: Lesley | September 23, 2009 8:40 AM
Frank,
Now what would I do if the term "Fall" is outlawed with my way I was taught as a child of knowing how to set my clocks for daylight savings
"Spring Ahead .. Fall Back"
:-)
FR: Dunno. Spring ahead, autumn back? I always found that memory aid less than helpful. Spring back, fall forward always made just as much sense to me.
Posted by: F Smith | September 23, 2009 2:04 PM