Macbeth has recently met with the Weird Sisters who told him that he would become the Thane of Cawdor as well as King of Scotland.  Because he learns from Ross that he has, indeed, been given the title of Cawdor immediately following the Weird Sisters' apparent prediction, Macbeth quickly begins to believe that the second prophecy will come true as well.  He begins to desire the position of king, a role he never seems to have considered for himself before.  When Duncan names his son, Malcolm, the Prince of Cumberland and his heir to the throne, Macbeth is disappointed to say the least.  To himself, he says that he will either have to halt his progress to the throne now or jump over this step to becoming king.  He speaks to the stars, asking them to go dark so that no one will be able to see his "black and deep desires"; in other words, he now fully admits to himself that he wants the throne and everything that comes with it.  This also begins to foreshadow the terrible deeds of which Macbeth will be capable later on.