Question

can anyone explain theory of big bang and cosmic calendar

Answer 1

the universe originated billions of years ago in an explosion from a single point of nearly infinite energy density .
The Cosmic Calendar is a scale in which the 13.7 billion year lifetime of the universe is mapped onto a single year. 

Answer 2

Heya ...!!

Big bang theory is a theory that tells how universe, that is space time and matter was formed in the universe. This theory was derived mathematically from equations of general relativity by the Belgian monk Georges Lemaitre that gives a creation point of the universe. 

Chief features of Big Bang theory are :

1.) All points that comprise our universe was confined to a single point of infinite temperature, infinite density and known laws of physics does not hold at that point.  

2.) An explosion occurred at that point about 13.75 billion years ago and point began to expand, real time started. It can be thought as small marks on balloon being inflated.
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>>Cosmic Radiation or calendar is the radiation created by all stars in the form of U.V,X-Rays,Gamma Rays etc(When exposed to it it can cause cancer by changing the cell structure dramatically and damaging the body),even planets create radiation but only in a minute ammount.Our eath also releases radiation but it does not effect us as it is very weak.
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hope helped...!!