It is entierly conformative that the jyotis´a1 divided into three branchies.-siddhãnta,samhitã and horã.Subsequently there are advancement in the names as gañita(siddhãnta),jãtaka(horã),samhitã.So the entire word jyotis´a can be name as Astrology.
1
The work of astronomy which become gradualy useful to decode dates,knowledge about sesons,nature migh have been an independant subject and the ephemeris i.e. "PANC´ãNGA" was the great discovery of that time!
From history of the astrology it is found that 2637BC in china people had knowledge about the ephemeris.While in india jyotis´a period is 1500 BC aproximately commenly accepted.But actualy what I want to prove that such type of method to dicide auspious period might have been gradualy devoloped to the nature related things may be name "muhurt sh´stra"2.As vacaspati Himmatram Jani says-Vedik people in atharva vedik period were using the word "pun´yarha".i.e. The auspicious time in which time period be successful one.Such type of pun´yarha time period which we decide by calculating days seasons etc.by the tools of tithi ,karan´a,nakshatra.30th part of ahoratra (day+night) had a sajn´a "muhurta".
The construction of Tithi patra(PANC´ãNGA) i.e.Ephemeries was made on the base of the book that was vedang jyotis´a.gradualy durring the vedik time
and in sraut sutra and gruhya sutra yoga and for the marriage time kala nirnaya i.e. muhurta seems to be used.To decide muhurta ,the laws are found in the book of Atharvavedang jyotis´a.While to know tithi naxatra etc. knowledge the book is yaju´ jyotis´a.
In essensial period or in hurry the people were used to do the work with blessings from brahmins.So "punyah vachan" the word right now brahmins use in karmakand
According to dr.jani after the period of yaju´ jyotis´a , Atharvavedang jyotis´a was established and after this punyah subject was devoloped i.e. MUHURT SHASTRA.