The moon also represents mystery and promise. It takes on a symbolic meaning that transforms it into a magical wishing star.  When Amanda and Tom have their playful discussion in Scene V.

The fact that Amanda and Tom discuss the moon in this scene, and that it is done in a very light, casual way, it allows for a pleasant moment between Amanda and her son.  The reader also sees Amanda's superstitious side when she asks her son:

"Have you made a wish on it yet?" (Williams)

Amanda asks her son what he wished for and he tells her that it is a secret. Then Amanda tells him that she won't reveal her wish either, that she can be mysterious too.  But she does reveal her wish:

"No I don't have secrets.  I'll tell you what I wished for on the moon.  Success and happiness for my precious children.  I wish for that whenever there's a moon and when there isn't a moon, I wish for it." (Williams)

The exchange between Amanda and Tom in the beginning of this scene sets up the revelation that Tom has found a gentleman caller to invite over for dinner, just as his mother asked him. 

In my view, I think that Tom is a bit sarcastic and uncaring with regard to his mother in this scene.  He acts very cavalier about the whole gentleman caller thing when he knows that his mother is very serious about finding Laura a husband.

The moon for Amanda represents reminiscence and nostalgia about her youth; she also sees in it the possibility of romance and love for her daughter Laura.

For Laura, it represents the inaccessible aspect of romance instead of nostalgia. Laura has never had a real boyfriend, and after her false hopes about Jim, she is not deluded about her not so certain future.

For Tom, it represents restlessness and the longing for escape and adventure. Tom goes out at night, either to the movies or on sporadic drinking bouts. When Amanda exasperates him, he finally explodes, and jeers at her to fly off with all her gentlemen callers over the moon, much as a witch on a broomstick.

For all three of them, the moon represents longing - an unsatisfied desire welling up from within.