The day for the Brahmotsvam is selected on the day of Prathishta day of the temple. or the birthstar of the temple diety it can be conducted in the two ways one SHRADOTSVAM OR KAMYOTSAVAM ,
Brahmotsavam means GRAND CELEBRATION OR FUNCTION PERFORMED BY BRAHMA ,
once Lord Indira killed one Brahmarakshasa for that reason he was Incurred Brahmathidosham. To relieve him from that in Lord Brahma himself hold Sriman Narayana on his head during the special Ritual bath so called AVABRIDASNANAM (THEERTHAVARI).
BECAUSE OF IMMENSE OF CLEANING POWER OF BRAHMOTSAVAM this utsavam is periodically done in the temples, to wash away all the sins incurred in the community. it is said that first brahmotsavam was held by Brahma himself t0 Lord vishnu ,it is also common that every Brahmotsvam is still watched by Lord Brahma. Brahmotsavam function is performed for 9 days It is not only the temple ritual but it is the grand function of the whole town. It begins with Ankurarpanam (planting of 9 grains in the soil) to take this soil VISHVAKSENA (chif security officer of Lord vishnu)goes to collect the soil known as MRITHSNKRAHANAM.
