According to our weather person, Fall starts on 9/23/11, How?

[Gannet]

I assume this is the right forum to ask this question

Based on what I think I know, the Earth completes one full orbit of the Sun in approximately 365.25. Every four years we have a Leap year that adds one day. This I understand. What confuses me is how can Fall begin more than 24 hours after 9/21/11 23:59:59.

I remember after submitting that I didn't taking into account time zones. I live on the East Coast and we our on DST and next year we have a Leap Year

 

[mesosphereman]

The average date of the Fall equinox is Sept 22 or 23, not Sept 21. This is really just a matter of counting days in our calendar months, and equally dividing the year into four quarters.

 

[Gannet]

Thanks mesosphereman, I never thought of that

 

[256bits]

It is a little more complicated than dividing the calendar into 4 slices, as the slices are not of equal length or number of days. March equinox to June solstice is around 93 days, the same for June solstice to September equinox. From Sept equuinox to December solstice it is about 90 days, and again the same for december soslice to the March equinox.
The reason being is that the Earth's orbit is an ellipse, and when the Earth is farthest from the sun during the northen hemisphere's summer, it revolves a bit more slowly than during the winter in the northern hemisphere.

A good site that explains the equinox and the solstice is
http://www.timeanddate.com/calendar/september-equinox.html

 

[Gannet]

Thanks 256bits

That is a great site. I added to my favorites

I notice that they had some Septermber equinox as late as September 24th in 1931 and that the next time it will be on September 21 is in 2092.