Why is Janmashtami (Ashtami Rohini) celebrated on neither Ashtami or Rohini?
The Janmashtami of 2016 is celebrated on 24th of August. If one look into the calendar, the star is Bharani and the Thidhi is Sapthami. So who decided this date to be the auspicious one? The answer is, the Thidhi has to be considered for Janmashtami, not the star. As Sree Krishna was born midnight, we consider the day on which the Thidhi will be Ashtami on midnight. So, 24th August 2016 is Sapthami for most part, but will be Ashtami on midnight when the auspicious birth took place and so the date is considered as Janmashtami.