Leonard Nimoy did indeed take the "live long and prosper" hand
position from the Birkat Kohanim ("Blessing of the Priests")
traditionally said over the congregation by the "priests" (which is
to say, men descended from priests, the Jewish priesthood having been
otherwise unemployed since the Second Temple was destroyed two
milennia ago) and --less traditionally, I believe -- said (without
the hand position) by parents in the home on Friday nights as part of
the blessing of the children. The curious can look at the hand
position on the web, e.g.:
http://altreligion.about.com/library/glossary/symbols/bldefsbirkat.htm
http://en.wikipedia.org/wiki/Priestly_Blessing
Like a lot of Jewish ritual, there are differing accounts of what it
means. Some say the hand position represents the letter shin, for
"Shaddai," one of the names of God. There are other explanations:
http://judaism.about.com/od/shabbatprayersblessings/f/bless_kohanim.htm
I have never been able to get my fingers into that position, but I'm
not a kohen, so it doesn't matter.
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