India uses the Gregorian calendar for all practical purposes - where the point of reference is the birth of Jesus Christ. But for religious observations and their time of reckoning, Hindu astronomy generally follows the solar and lunar calendar system. This system of keeping time has been followed for around 2,000 years - it is believed. And the timing of the Kumbh Mela is decided by the conjunction of planets, sun and moon.

The Kumbh Mela is associated with the solar cycle, and its ritual bathing, with lunar phases. Tracking the passage of days comprises a mix of the solar and lunar calendars - the former being the time taken for the sun’s return to the same reference point in its path through the sky, and the latter measuring the moon’s successive return in relation to the sun. The Kumbh is held at Allahabad when Jupiter enters Aquarius and the sun and moon move into Capricorn. Auspicious bathing days follow similar planetary conjunction - the previous one, on January 14, occurred when Jupiter was in conjunction with Aries and the next, today, would be on the new moon day of this conjunction. The moon is seen as a powerful symbol of regeneration.

It is also seen that the Kumbh Mela occurs generally at intervals of 12 years - the mean time of revolution of Jupiter. On some occasions, the Kumbh takes place at an interval of 11 years. The reason is that the correct mean period of Jupiter is slightly less than 12 years - it is about 11.86 years. Hence it makes 7 revolutions in a period of about 83 years as against the period of 84 years calculated on the basis of a revolution period of approximately 12 years, and so difference of one year happens at this long interval.

Though the astrological combinations effecting Kumbh are based on Hindu astrology, modern scientists now see a relation between the Kumbh Mela and the Sun. There is a school of astronomers, which sees a relationship between the timing of the Kumbh and the different stages of the solar cycle. The measured cycle of sunspots - abnormally cold areas, many times the size of the earth, on the sun’s surface, emitting large amounts of radiation and charged particles - seem to form a pattern matching roughly that of the Kumbh cycle. It interests astrologers; astronomers have been studying the pattern, for some time.

For the pilgrims to Kumbh - the Hindu calendar, which reaches back through millennia - tracks the movement of sun, moon and stars through the heavens. And it is from here that the word spreads, literally, in this still largely unlettered country. Through the land and through villages, through homes, the knowledge of when the next Kumbh configuration is to come. And Hindus flock, without any central call, in response.