Upakarma
Upākarma "Beginning" (Sanskrit: उपाकर्म), also called Āvaṇi Aviṭṭam (Tamil: ஆவணி அவிட்டம்) and Janivārada Huṇṇime (Kannada: ಜನಿವಾರದ ಹುಣ್ಣಿಮೆ), is a Vedic ritual still practiced by modern Hindus of the Brahmin caste.
Upākarma is conducted once a year during the Dhaniṣṭhā nakṣatra of the Hindu calendrical month Śrāvana, when Brahmins ritually change their upanayana thread accompanied by relevant śrauta rituals, making śrāddha offerings to the rishis, whom Hindus believe composed the Vedic hymns. The day, also called Śrāvana Pūrnima "Full Moon of Śrāvana" in other parts of India, usually occurs the day after the Śravana nákṣatra, which also marks the Onam festival of Kerala.
On the following day, usually coinciding with the Raksha Bandhan festival in Northern and Central India, the Gayatri Mantra is recited 1008 times.
Brahmins belonging to the Samaveda do not perform upakarma rituals or change their thread on this day but rather on Bhādrapada chaturthi, the fourth day of the month Bhādrapada. Shukla Yajurvedic Brahmins of North India and Odisha do upakarma the previous day if the full moon spans two days.
Read more about Upakarma: When Is Upakarma Observed?, Upakarma Variation, Upakarma in Eclipse/Solar Sankramana, Legend, Significance, Procedure of Avani Avittam, Inner Meaning