Hello, John and Doves,

 

Since the vernal equinox was on March 20 at 23:21 UTC, the correct day for Nisan 1, 5771 was April 5, 2011, having begun at twilight, April 4, 2011.  http://earthsky.org/astronomy-essentials/everything-you-need-to-know-vernal-or-spring-equinox

 

Thus, the correct day for Pentecost is Sivan 6, 5771/June 8, 2011.  http://www.aish.com/h/  You can download the calendar at the bottom of the page.  Note that this is a strictly Jewish site, so they have no ax to grind.

 

Baruch HaShem Adonai,

Mike C.