According to the astrological calculations, event of Kumbh (a festival occurring every 12 years) takes place in 4 ways as follows:
1. In the event of entrance of Jupiter in Aquarius (Zodiac sign) and entrance of Sun in Aries (Zodiac sign) Kumbh festival is held at Haridwar.
” पद्मिनी नायके मेषे कुम्भ राशि गते गुरोः ।
गंगा द्वारे भवेद योगः कुम्भ नामा तथोत्तमाः।। “
2. In the event of entrance of Jupiter in Aries circle and entrance of Sun and Moon in Capricorn Kumbh Festival is held at Prayag on the lunar conjunction day (अमावस्या)
” मेष राशि गते जीवे मकरे चन्द्र भास्करौ ।
अमावस्या तदा योगः कुम्भख्यस्तीर्थ नायके ।। “
Kumbh Festival is also held at Prayag in the event of entrance of Sun in Capricorn and entrance of Jupiter in Taurus .
मकरे च दिवा नाथे ह्मजगें च बृहस्पतौ कुम्भ योगोभवेत्तत्र प्रयागे ह्यति दूलर्भ:
3. In the event of entrance of Jupiter in Leo Kumbh Festival is held at Nasik on the bank of river Godavari
” सिंह राशि गते सूर्ये सिंह राशौ बृहस्पतौ ।
गोदावर्या भवेत कुम्भों जायते खलु मुक्तिदः ।। “
When Jupiter, Sun and Moon enters in Cancer on lunar conjunction (Amavasya – last day of the dark half of a month) then also Kumbh Festival is held on the bank of river Godavari.
” कर्के गुरू स्तथा भानुचन्द्रश्चन्द्रर्क्षगतस्था ।
गोदावर्या तदा कुम्भो जयाते Sवनि मण्डले ।। “
4. In the event of entry of Jupiter in Leo and entry of Sun in Aries Kumbh Festival is held at Ujjain.
” मेष राशि गते सूर्ये सिंह राशौ बृहस्पतौ ।
उज्जियन्यां भवेत कुम्भः सदामुक्ति प्रदायकः ।। “
When Jupiter enters in Libra and Sun & Moon remain together on Kartik Amavasya (8th month of Hindu year) then also Moksha Dayak (Free from all bonds) Kumbh Festival is held at Ujjain.
” घरेसूरिः शशि सूर्य कुह्मं दामोदरे यदा।
धरायां च तदा कुम्भों जायते खलु मुक्तिद: ।। “
” अहं राष्ट्री संगमनी वसूनाम्श् “
Why Kumbh Mela is held after 12 years only?
Answer to this is in the Samudra Manthan (Sea Churning). Jayant took 12 days to carry the nectar kalash to the heaven. One day of Gods was equal to one year of the humans. It is why that in the sequence of stars state at 12th year Kumbh is held at festival places.