Why is the comparison to the stars another example of foreshadowing?

The imagery of the stars is compared to fate or destiny throughout Shakespeare's Romeo and Juliet. Like today, in Renaissance England stars were associated with astrology, a way to predict an individual's future based on the alignment of those stars on the day they were born. Shakespeare opens the play by calling the title characters "star-crossed lovers," implying that fate has determined that nothing good can come of their relationship. In fact, the prologue foreshadows most of the tragic events in the play. In act I, scene 4, Romeo reintroduces the stars in a short aside where he relates a dream which suggests that his attendance at Capulet's party will lead to his death:

I fear too early, for my mind misgivesSome consequence yet hanging in the starsShall bitterly begin his fearful dateWith this night’s revels, and expire the termOf a despisèd life closed in my breastBy some vile forfeit of untimely death.


His words foreshadow future events because his meeting Juliet at the party and their whirlwind romance will ultimately lead to his suicide on the floor of Capulet's tomb. Both Romeo and Juliet will foreshadow death in various parts of the play. Before he marries Juliet, Romeo says,


Do thou but close our hands with holy words,Then love-devouring death do what he dare,It is enough I may but call her mine.


Juliet seems to foreshadow Romeo's appearance in the Capulet vault at the end of the play in act III, scene 5, saying,


O God, I have an ill-divining soul!Methinks I see thee, now thou art so low,As one dead in the bottom of a tomb.Either my eyesight fails or thou lookest pale.




Later in the play, after Romeo has learned that Juliet is supposedly dead, he again references the stars, saying, "Then, I defy you stars," implying that he will not simply let fate take his love away but will also commit suicide by her side.