There has been much talk today about the end of summer. And part of this talk has been about the lack of summer this summer had. It has been a very strange year, meteorologically speaking. Cooler than normal summer. Warmer than normal winter. Very strange spring.
Now the cool summer comes to a close with the autumnal equinox. It happens this year at 03:09 September 23 UTC (3:09 am on Sept 23, coordinated universal time). This puts it at 21:09 September 22 MDT (9:09 pm on Sept 22, mountain daylight time).
Of course, people always ask about the 12/12 day-night split. By definition, the equinox occurs when the sun crosses the equator. This does not mean, however, that day and night are everywher of exactly equal length. The farther from the equator one travels, the longer the day. The sun takes longer to rise and set, since it moves not vertically through the sky, but diagonally with a horizontal component.
So I hope you have enjoyed what little there was of summer. Autumn will be here soon, and then winter.