Saying aavani avittam is wrong. We have to tell this as sraavana pournami which is correct. soura month and chandramaana monh are there. Soura month is based on thithis. from one amavasai to another amavasai is one month which we are telling chithrai, vaikasi etc,or mesham,rishabha month etc; Based on 27 nakshathra month is coming as chaithram, vaisaagam,jyestam,aashaadam, sraavanam, pathrabadam,aashvinam, karthigam, margasiram, pousham,maagam and paalgunam.
In this chaandramana kramam sraavana month starts on 23rd july. so this month is sraavana month and on pounami day of this sraavana month if there is no other dosham aapasthambigal must perform upakarma. Rig vedhis must perform on sraavana month thiruvonam (sraavanam) star day upakarma. samavedha people must do on hastha star day in pathrabadha month.
In majority, the upakarma will come only in aavani pournami. so it is called as aavani avittam. on this day vedam studying is begining. for six months that is upto 25th january 2013 we can learn vedams. this year. For other six months we have to study 1. siksha. 2. vyaakaranam. 3. chandas. 4. nirutham. 5. astrology. 6. kalpa soothram. Then once again starting learning vedams from sraavana pournami day.