Here is your short paragraph on Chitra Pournami:
This is the full moon day in the month of Chittirai (April-May) and is an auspicious occasion for the final day function (tirttavari) of the annual festival in several temples of Tamil Nadu.
If Chitra Pournami happens to fall on a Thursday, Saturday or Sunday, it is regarded as very sacred. Myth tells us that Lord Indra, the celestial lord wanted to emaciate his sin by worshipping Siva at Madurai and caused to dig a tank wherein, by the grace of the Lord, golden lotus flowers appeared which he used to worship the Lord on Chitra Pournami day.
So this festival is observed with great enthusiasm at Madurai.