Yama, Yami (personification of the river Yamuna) and the Aśvinī Kumāra, are popularly referred as the siblings of Lord Śani (शनिदेव ) .
What might be lesser known, are Bhadrā (भद्रा ) and, Tapatī (तपती ) are also Shani's siblings. Again, Tapatī maybe understood as the personification of the Tapti (or Tapi) river. The starting lineage of Kuru can be traced to her.
Bhadrā is more shrouded in mystery, to even place her as some deity or other exalted entity. As a guess, I have heard from the elders and read a lot, is the concept of a recurring inauspicious time frame, which is also called as Bhadrā - kāl (भद्रा - काल).
Generally, to begin any new auspicious work, one has to make sure that all the planetary positions are appropriate and conducive, thus yielding a Śhubh Muhūrta i.e. A favourable or propitious period. All new works must be done on this propitious time frame, which is determined as per the Pañcāṅga calculations by a competent astrologer - jyotiṣika. Now, if, by chance the calculated propitious time frame coincides with a Bhadrā - kāl, then the propitious period is rendered inauspicious to either Start and End a new auspicious work. For example: Each year during Rakṣābandhana, a Bhadrā - kāl, is invariably observed, which forbids the Rakṣāsutra tying up ritual for that period of Bhadrā.
So, two questions:-
Is the astrology Bhadrā - kāl, actually same as the Lord Śani's sister Bhadrā ? What are the actual valid scriptural references for the various stories (linked above) related to the origin and life of Bhadrā?
What happens when a Bhadrā - kāl happens in Abūjh Muhūrta (A.B.)? As I discuss in this question, that A.B, by definition are infallible and Bhadrā by definition invalidates any kind of auspicious moments. So, won't it create a paradox? Or, is it that generally the A.B days are choosen such, that they don't fall on any Bhadrā - kāl days?