B’Midbar / Numbers 6:22 And the LORD spake unto Moses, saying, Speak unto Aaron and unto his sons, saying, On this wise ye shall bless the children of Israel, saying unto them, “The LORD bless thee, and keep thee: The LORD make his face shine upon thee, and be gracious unto thee: The LORD lift up his countenance upon thee, and give thee peace. And they shall put my name upon the children of Israel; and I will bless them”.
In some communities it is customary for the Kohanim (Priestly descendents of Aharon [Aaron]) to raise their hands and recite an extended chant before reciting the last word of each phrase. There are different tunes for this chant in different communities. Aside from its pleasant sound, the chant is done so that the congregation may silently offer certain prayers during each individual blessing of the Kohanim.
In the mid-1960s, actor Leonard Nimoy, who was raised in a traditional Jewish home, used a single-handed version of this gesture to create the Vulcan Hand Salute for his character, Spock on Star Trek. He has explained that while attending Orthodox services as a child, he peeked from under his father’s tallit and saw the gesture; many years later, when introducing the character of Mr. Spock, he and series creator Gene Roddenberry thought a physical component should accompany the verbal “Live long and prosper” greeting. The Jewish priestly gesture looked sufficiently alien and mysterious, and became part of Star Trek lore.