RahuKalam (period of Rahu) has a very important place in Vedic Astrology. Certain parts of the day, called Rahu Kalam, are inauspicious periods and one should not undertake any auspicious work during these periods - especially any new undertaking. Rahu Kala changes according to day of the week and the time of sun rise and sun set. RahuKalam is calculated with help of Sun-Rise and Sun-Set time. The day duration from Sun-rise to Sun-set, at a particular location, is divided into eight equal parts. There is no Rahu Kalam during the first period of any weekday. Rahu Kalam is one and a half hour time each day of a week distributed at random in the week days.
Since the Rahu Kalam is dependent on the Sun-rise and Sun-set times therefore the time for Rahu Kalam differs from place to place.