Rahukalam is called the time period of Rahu. It is the time to which the Rahu period refers. Rahu Kaal denotes an inauspicious time period in each day. Doing any auspicious work in Rahu period is not considered favorable. In Hindu astrology it refers to a period of 90 minutes every day between sunrise and sunset. It is considered important in South India and its calculation and time period of Muhurtas are well known. However, routine tasks that have already started can continue normally in this period.
Rahu is a shadow planet and is the king of meteors in the nine mythological planets (navagrahas) mentioned in Hindu texts. In mythological texts, a demon named Shavarbhanu had propelled himself as a god during the churning of the ocean to receive Amrita from Mohini and had taken the nectar of deceit, so Lord Vishnu used his Sudarshan Chakra Asura was cut into two parts, Rahu and Ketu. Rahu is considered to be a male planet that tries to eclipse the Sun and the time period when Rahu affects the Sun is considered inauspicious.
Rahu period is considered in a predetermined manner during the scheduled time on different days of the week, but can also vary according to the time of sun rise. The time of Rahu period may also vary according to the time of sunrise at different places. The sunrise time is marked in the almanac and the 12 hours of the day are divided into eight equal parts. Rahu period does not occur in the first part of the day, (from 6 am to 7.30 pm) so this time is always auspicious and the remaining seven parts are divided according to each day.