In Śrīmad-Bhāgavatam it is stated that the rāsa dance took place on the full-moon night of the śarat season. From the statements of previous chapters, it appears that the festival of Govardhana-pūjā was performed just after the dark-moon night of the month of Kārttika, and thereafter the ceremony of Bhrātṛ-dvitīyā was performed; then the wrath of Indra was exhibited in the shape of torrents of rain and hailstones, and Lord Kṛṣṇa held up Govardhana Hill for seven days, until the ninth day of the moon. Thereafter, on the tenth day, the inhabitants of Vṛndāvana were talking amongst themselves about the wonderful activities of Kṛṣṇa, and the next day, Ekādaśī, was observed by Nanda Mahārāja. On the next day, Dvādaśī, Nanda Mahārāja went to take a bath in the Ganges and was arrested by one of the men of Varuṇa; then he was released by Lord Kṛṣṇa. Then Nanda Mahārāja, along with the cowherd men, was shown the spiritual sky.
In this way, the full-moon night of the śarat season came to an end. The full-moon night of Āśvina is called śarat-pūrṇimā. It appears from the statements of Śrīmad-Bhāgavatam that Kṛṣṇa had to wait another year for such a moon before enjoying the rāsa dance with the gopīs. At the age of seven years He lifted Govardhana Hill. Therefore the rāsa dance took place during His eighth year.
From the Vedic literature it appears that when a theatrical actor dances among many dancing girls, the group dance is called a rāsa dance. When Kṛṣṇa saw the full-moon night of the śarat season, decorated with various seasonal flowers—especially the mallikā flowers, which are very fragrant—He remembered the gopīs’ prayers to goddess Kātyāyanī, wherein they prayed for Kṛṣṇa to be their husband. He thought that the full-moon night of the śarat season was just suitable for a nice dance. So their desire to have Kṛṣṇa as their husband would then be fulfilled.