Rig Vedi Upakarma, or Rg Vedic Upa Karma, is the sacred thread changing ceremony observed by the Brahmin community that follows the Rig Veda – one of the four Vedas. In 2013, date of Rig Vedi Upakarma is August 20. It is observed during the Shukla Paksha (waxing phase of moon) of Shravan month and is also known as Rig Vedi Avani Avittam in Tamil Nadu and Kerala. The Gayatri Japam ritual is also observed on the day.
On the Thiruvonam Nakshatra day in Shravan month (July – August), Brahmins who follow the Rig Veda perform the sacred thread changing ceremony known as Yagnopaveetha Dharana or Janeyu Dharana. This ritual is part of ancient Vedic rituals and includes chanting of Mantras. Students also begin the study of the Vedas on the day.
This ritual is not observed by most North Indian Brahmin communities. But some priests and Brahmins observe such a ritual on the third of the Shukla Paksha of Bhadrapad month.
Special mantras are chanted while performing the Rg Vedi Avani Avittam ceremony. You can get the details of Rig Vedi Avani Avittam Mantras here.