Significance of Sathabhishekam

[Badri]

I am posting this on behalf of Shoba, but I would like info as well! Shoba is trying to put together a presentation on Indian Birthday celebrations and needs this info.

In many Indian Hindu households, the 80th birthday of a grandfather is a grand gala event! It is known as Sathabhishekam, and it is an occassion for the entire family to gather around the (great)grandparents. In fact, even total strangers walk in when they hear a Sathabhishekam is being celebrated to fall at the feet of the elder and seek his blessings.

Last year, I had the good fortune of being at my grandad's 80th b'day celebrations, and it was a fun event, alright!

But what is the significance of this event? Why is it celebrated with such gusto? Is reaching 80 such a big achievement which is why it is being thus feted? Also, why is it called Sathabhishekam? They say the person has seen a 1000 full moons since his birth; then why not call it Sahasra abhishekam (sahasra=1000 in sanskrit) or something similar?

Or is it actually Sadaabhishekam, as in
sada = always, and Abhishekam = auspicious?