Varshikotsvam is an annual festival celebrated for 1 day in the month of Ashadha (June-July) to commemorate the appearance of the Deities.
The Supreme Lord descends in the form of Deities so that we get an opportunity to serve Him. The Lord is transcendental to our mundane senses. He cannot be seen with our present eyes, nor can He be heard with our present ears. To the degree that we have entered into the service of the Lord or to the proportion to which our lives are freed from sins, we can perceive the Lord. But even though we are not free from sins, the Lord is kind enough to allow us the facility of seeing Him in His Deity form in the temple.
In 2009, the Supreme Lord descended in Valmiki Nagar, Thiruvanmiyur to bestow His mercy upon us and this occasion is celebrated by the devotees as Varshikotsvam.