Why is kheer kept under moonlight on Sharad Purnima?

According to Vedic cosmology, the moon shines with all 16 of its kalas (phases) on the auspicious night of Sharad Purnima and its rays are believed to carry special medicinal and divine properties. People leave 'kheer' (a preparation of milk and rice) under this moonlight with the belief that it will absorb the divine energy and become 'amrit-like' (nectar).