" A water body made in the shape of a constellation, which looks like a water diviner in a town where one of the biggest festivals is celebrated to signify the arrival of water in major rivers. The connection between Mahamaham tank and water and the constellation Aquarius are there for all to see. But, an answer to the question of 'why go to this length?" eludes me.
Your research on the subject is really an excellent piece of work ! Kumbakonam is an ancient town where vedic scholars and astronomers lived and live even today ! I learn that on the particular day of Mahamaham, every 12 years, the constellation of 3 planets (what are they?) takes place and it is said, that the effect of this constellation falls on this temple tank during that day which is believed to give divinity to the water which perhaps purifies all your sins!
I have posted the articles in a new blog site - http://emeraldfields.wordpress.com/ - with larger pictures. Would be happy to take the questions. Kannan Adityan