Celebration of the 59th Birthday are called UgraRath Santhi.
According to the Vedas, at 60 a man has reached the halfway mark of his actual span of life, which is 120 years. And according to Hindu numerology, six is not a favourable number and 60 is a point in life when the ruling planet of a person may have an adverse effect on his life. The person performs a religious shanti, mainly to invoke peace, ensure good health, and longevity.
Bheema Ratha Santhi
The 70th Birthday of a person is celebrated as the Diamond Jubilee and is very important. Celebration of the 70th Birthday are called Bheema Ratha Santhi.Modern people consider that beyond the age of 70, one cannot accomplish anything in life. However, contrary to this, beyond the age of 70 years, the zeal and dynamism in a person actually increases. It is at this point of time that the Atma Shakti manifests itself. Prior to this, they just behave in an ordinary manner. Beyond 70 years of age, their Mental Power and Will Power takes a new direction.
Celebration of the 77th Birthday are called Vijaya Rath Santhi.
Celebration of the 81th Birthday are called Sathabisheka Santhi.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
The celebration is for the birth of a son's son's son(great grand son through sons).