Why are Romeo and Juliet called "star-crossed lovers"?

A pair of
star=crossed lovers take their life,
Whose misadventured piteous
overthrows
Do with their death bury their parents" strife.
(1.1.6-8)

In the Prologue
of Romeo and Juliet that is spoken by the Chorus, who introduce the
play to the Elizabethan audience, the term "star-crossed" would be one quite familiar to
these Elizabethans. For, the stars are part of the Chain of Being. When one part of this
chain is upset, as in the stars, then there is disorder and chaos. So, when the stars
are taken out of their order, things go awry and fate changes the order of
things.

Therefore, when Romeo and Juliet have their stars
taken out of order and "crossed," they become fated lovers, lovers to whom misfortune
will come. Thus, their lives contain a destiny that will prove tragic for them. In
modern times, one would say that they have bad luck, such as when they meet and their
families are in a feud against one another; or, when Romeo happens upon Mercutio and
Tybalt fighting and he inadvertently kills Tybalt; or, when John cannot get the Friar's
message to Romeo because Mantua is quarantined; or, when Friar Laurence runs out of the
catacombs and Juliet is left alone to her fate.