Upakarma means the beginning or arambha of something auspicious. Generally it is associated with the beginning of the learning of the Veda.
But apart from that it is also associated with the changing of the Yajna pavit of the Brahmans or the changing of the sacred thread along with the Shrouta recitals.
The Yajur Veda Avani Avittam as it is called or the Yajur Veda Upakarma is practiced by the YajurVedi Brahmins of Tamil Nadu, Kerala, Andhra Pradesh and Karnataka. The Yajnapavita Dharanam is the major observance of that day. From this auspicious day the Yajurvedi Brahmins also start reading the Yajur Veda for the coming 6 months.
It is considered to be extremely auspicious as it is believed that on this day Lord Hayagriva, who is considered to be the Lord of Knowledge restored the Vedas to the Gods from the demons.
In 2017, the date for the Yajur Veda Upakarma is July 28th, Friday. The Yajurvedi Brahmins observe the Upakarma on the Shravan Purnima, which is full moon of the Sharavan month.
How is the Upakarma celebrated?
In Tamil Nadu this is known as Avani Avittam and in Andhra Pradesh this is known as Jandhyala Purnima. On this day, after offering oblations to The Devas, all the sages and the ancestors an offering of pazham, vetrilai, paakku is done. Then a dakshina is given to the Guru to seek blessings. The sacred thread is supposed to protect the devotees from all kinds of illness and enemies. A Mahasankalpam or a great vow is taken for the washing away of all the sins of the past year. After this the Brahmins, take a holy dip in a water body and wear the new yajna pavit or the sacred thread.
Those following the Yajur Veda Upakarma will do so on the month of Thiruvonam nakshatra.
What is the procedure of the Upakarma?
At the outset, the Rishi Tharpanam or the offering to the Rishis is done. Brahmins bachelors then do a Samitha Daanam after the Mahasankalpam. After that with the aid of the family priest the Kanda Rishi Tharpanam is done. A light meal is had at dinner. The morning thereafter, the Gayathri Japam is done, which is the chanting of the Gayathri mantra of 108 to 1008 times.