It is a common custom followed to tie a black or black and yellow thread around the the waist of a Newborn at the 28th day.Initially this custom was followed exactly at the 28th day after the child was born.Now since people are pre-occupied with work this ceremony is conducted on a Holiday and extends to 29th or 30th day.Majority of the people do not know the significance of this ceremony why it has to be on the 28th day.
There are 28 stars associated with our system starting with Aswathy,Bharani and going up-to Abhijith (28th Star.2.5 Nazhika). Normally Astrologers take only 27 stars into consideration because Abhijith has a short time duration when compared to other stars.But Abhijith is strong during the period when it is present.28 days constitute a Chandra Masa(Moon Month). In 28 days these stars will come face to face with the Moon one by one.The rays from the star will get mixed with the rays of the Moon and Somam( A subtle matter in the form of liquid ) which is present on the surface of the moon and fall on the earth in all living and non living beings.Moon is also called Soman because of presence of Somam. A combination of the rays from the star of that day,Moon and somam fall on all human beings at night.These rays get solidified when sun rays fall on it and become a grain which is very subtle.This grain is so subtle that several grains may be confined to the point of a pin.This grain is called Pithru Pindam as per Rig Veda.Pindam is the smallest form of matter.The Scientists from West have named this " Paternal mass". Pithru Pindam got from 28 stars in 28 days forms a jelly like seed called Tandulum.In a normal person after 16 years of age this Tandulum will mix with blood to produce the necessary count for reproduction.This process exists in plants too and is responsible for their growth.This is the reason why Moon is also called" Aushadheesan".
When a baby is born 21 Pithru Pindam will get transferred to the child from the father.The remaining 7 remain with the father.From the second generation to 3rd,4th,5th,6th and 7th generation 15,10,6,3 and 1 are transferred. This is how heredity of a person spans to 7 generations.The Vedas have already stated the genesis long back.
For a newborn 28 days signifiy 28 Pithru Pindam which binds 7 generations and the newborn is indebted to previous 7 generations. It has been already stated that by the doctors "Ancestral discipline of the successor-ship is in 7 ancestor sections". Black thread signifies that you are bound to the world. Also, the color of Thamasa Gunam is black.Yellow thread signifies your duty to free yourself from ancestral bondage.Yellow color has the property to overcome difficulties.This explains why it is important to conduct the thread ceremony on the 28th day and not on any other day.
Concept of 28th Day Thread Ceremony for Newborn taken from the speech of Jagadguru Swami Sathyananda Saraswathi Tiruvadikal. Listen to the concept in Swamiji's own words below.http://youtu.be/UtyCUCiLTyo