The moon is a recurring element, or motif, in Carmilla. In literature, the moon is traditionally associated with mystery, transformation, and illumination. The moon often appears in this novella during scenes that occur at night, casting an eerie and mysterious light over the story's landscapes. The moon also enhances the setting's Gothic atmosphere, all in all contributing to the sense of foreboding and uncanniness that occurs all throughout the narrative.
The moon, with its many phases, often represents transformation and duality, as well. This duality is reflected in the contrasting, complex nature of Carmilla herself, who embodies both allure and danger. The moon's presence in the narrative underscores these dualities.
In Chapter 2, Laura describes Mademoiselle De Lafontaine's beliefs about the significance of the moon:
Mademoiselle De Lafontaine [...] now declared that when the moon shone with a light so intense it was well known that it indicated a special spiritual activity. The effect of the full moon in such a state of brilliancy was manifold. It acted on dreams, it acted on lunacy, it acted on nervous people, it had marvelous physical influences connected with life. Mademoiselle related that her cousin, with his face full in the light on the moon, had wakened, after a dream of an old woman clawing him by the cheek, with his features horribly drawn to one side; The moon, this night, she said, is full of idyllic and magnetic influence.
The image of the moon's luminosity suggests a powerful, almost ethereal quality. Mademoiselle De Lafontaine associates the moon with special spiritual activity, heightened emotional states, strange dreams, and increased mental instability.
The story Mademoiselle tells about her cousin and the image of an old woman clawing him on the cheek is striking and unsettling. The chilling, eerie image hints at the potentially transformative or disturbing effects of the moon's influence. In creating this image, Le Fanu also sets up Carmilla's mysterious appearance, which occurs soon after Mademoiselle makes her claims about the moon's powers.