The moon is mentioned often during A Midsummer Night's Dream and, as the title suggests, much of the play takes place by moonlight. Theseus first refers to the moon at the very beginning of the play, where it simply represents a month. When the moon is next mentioned, it is a symbol of chastity. This is one of the most common associations with the moon, as the Roman moon goddess, Diana, was the patron of unmarried girls. Theseus tells Hermia that if she does not marry Demetrius, she will have to die or become a nun,
Chanting faint hymns to the cold fruitless moon.
Oberon recognizes the same symbolism when he alludes to "the chaste beams of the watery moon," and Titania later reinforces this link between the moon and chastity.
The play ultimately subverts this traditional symbolism, since the moon also plays an important part in the tale of Pyramus and Thisbe. The amateur presentation of this play makes everything in it ridiculous, including the moon, which is suddenly inhabited:
All that I have to say, is, to tell you that the lanthorn is the moon; I, the man in the moon; this thorn-bush, my thorn-bush; and this dog, my dog.
The actors have pointless arguments about whether the actor who is playing the man in the moon should really be inside the lantern that represents the moon. By the end of the play, the moon has become as bright as the sun, as Pyramus observes,
Sweet Moon, I thank thee for thy sunny beams;
I thank thee, Moon, for shining now so bright.
This suits the riotous, anarchic nature of the final scene. The goddess of chastity has no place amidst all the now-married couples, and the cold, silvery moon has become as hot as the sun.