Katarchic astrology is the application of horoscopic astrology

Horoscopic astrology

Horoscopic astrology is a form of astrology that uses a horoscope, a visual representation of the heavens, for a specific moment in time in order to interpret the inherent meaning underlying the alignment of the planets at that moment...

 to determine an auspicious moment to begin a venture or undertaking, otherwise known as electional astrology

Electional astrology

Electional astrology, also known as event astrology, is a branch found in most traditions of astrology in which a practitioner decides the most appropriate time for an event based on the astrological auspiciousness of that time...

, as well as to interpret the auspiciousness of an inception that has already taken place. The latter application is more commonly referred to as inceptional astrology in modern times, although in the Hellenistic

Hellenistic astrology

Hellenistic astrology is a tradition of horoscopic astrology that was developed and practiced in Hellenistic Egypt and the Mediterranean, whose texts were written in Greek , mainly around the late 2nd or early 1st century B.C.E...

and Byzantine traditions the term katarchē was used to refer to both electional astrology as well as what modern astrologers refer to as inceptional astrology.