Weekdays or Tithis

[Guest guest]

Namaskar,

 

Various people perform some specific rituals or vratas on a particular weekday,

however I have a basic question how do we know that Sunday is really Sunday i.e.

the day connected to Sun.

 

Afterall the current calendar has been adjusted a lot of times in past

millenniums and also the starting point would make a difference too.

 

However we know that a particular tithi is really that only based on Moon phase,

so probably they are a better reference point.

 

Please advice, I may be completely off my bearing but better to understand the

basic reasoning.

 

Regards,

 

Ashish