2010 Summer Solstice
June 21 at 7:28 a.m., eastern daylight time.
   (June 21, 11:28 UT*.)

2010 Autumnal Equinox
September 22 at 11:09 p.m., eastern daylight time.
   (September 23, 03:09 UT*.)

2010 Winter Solstice
December 21 at 6:38 p.m., eastern standard time.
   (December 21, 23:38 UT*.)

* UT = Universal Time (Greenwich Mean Time)

Read an excerpt from Machaelle's Perelandra Garden Workbook (Chapter 15, pages 181-188)
that explains The Solstice and Equinox Cycle.