There are several auspicious days in the Vedic or Vaisnava calander year in honor of mother Ganga's pastimes. They are Aksaya-trtiya, Ganga-saptami, also known as Jahnu-saptami, Ganga-dushara, also known as Sri Ganga-puja, and Sri Ganga Sagara Mela.
Aksaya-trtiya appears in the month of Vaisakha (April/May) on the 3rd day of Sukla-paksa, or the waxing fortnight of the full moon. In the Matsya Purana, as quoted from the Sri Hari-bhakti-vilasa, the following is stated: "On the third day of the bright half of the month Vaisakha, the Supreme Lord Janardana created the grain of barley, started the cycle of Satya-yuga, and made Tripathaga Ganga desend to the earth from Brahmaloka."
Ganga-saptami or Jahnu-saptami also appears in the month of Vaisakha on the 7th day of Sukla-paksa, or the waxing fortnight of the full moon. After Ganga desended onto the Himalayas, the river entered the sacrificial arena of Jahnu Rsi and disturbed his meditation. As stated in the Padma Purana, Patala-khanda 85.49: "Formerly on the seventh day of the bright half of Vaisakha, Ganga was drunk through anger of Jahnu, and let out from the cavity of his right ear. "Also in the Narada Purana, Uttara-bhaga 41-37: "It was on the seventh day in the bright half of the month of Vaisakha that the Ganga was drunk up by Jahnu Rsi out of anger and cast off later on through his right ear. "There are other accounts regarding how Jahnu released Ganga. Therefore, Ganga also became known as Jahnavi, or the desendant of Jahnu.
Ganga-dushara (she who removes inauspiciousness) or Sri Ganga-puja appears in the month of Jyestha (May/June) on the 10th day of Sukla-paksa,or the waxing fortnight of the full moon.On this day,Maharaj Bhagiratha's desire of bringing Ganga to this mortal world was finally fulfilled as the sacred river descended from Lord Siva's blessed head at Mount Kailasa.The river Ganga then flowed through the Himalayas behind Maharaja Bhagiratha's chariot and passed through Jahnu Rsi's asrama.Afterwards,he sucessfully led Ganga to Rasatala,in the lower planetary system,to liberate the sixty thousand sons of King Sagara.As stated in the Narada Purana,Uttara-bhaga 40.21: "It was on the tenth day in the bright half of the month Jyestha,when the day of the week was Tuesday and the constellation was Hasta,Ganga descended to the mortal world." Ganga is also known as Bhagirathi,or the descendant of Bhagiratha.
Sri Ganga-sagara Mela occurs on Makarasankranti,or when the Sun enters Capricorn,which normally falls on the 14th of January every year.This festival is said to commemorate the day when Maharaj Bhagiratha led the Ganga to Rasatala to liberate the sons of King Sagara.The festival is observed at several locations on the banks of Ganga,but especially at the confluence of the Ganga and the Bay of Bengal,where Kapila Muni's asrama is located.
According to the local tradition in the Rishikesh area,Ganga-saptami is celebrated as the day Ganga descended from heaven to earth.Ganga-dushara,also known as Ganga-dasahara,marks the day the Ganga reached the plains of India at Haridvara. Ganga-dasahara means "Ganga destorys ten", so devotees bathe in the Ganga ten days prior to this day which destroys the sins of ten lifetimes.
The Narada Purana (Uttara-bhaga 38.17-19) describes when and where Ganga manifests herself within the three planetary systems during the Vedic calander month: "In the beginning of the dark half of the month, Ganga is present on the earth for ten days ending with sacred Amavasya (New Moon) day. From the first to the tenth of the bright half of the month, she is present in the netherworlds. Beginning with the eleventh day in the bright half and ending with the fifth day in the dark half, she is always present in heaven for ten days."
In other words: from the 6th dark day to Amavasya, Ganga is on the earth. From the 1st bright day to the 10th bright day she is in the netherworlds. And from the 11th bright day through Purnima (Full Moon) to the 5th dark day she is in heaven.
Note: There are different opinions regarding the appearance or desent of Ganga. The information provided for Aksaya-trtiya, Jahnu-saptami, and Sri Ganga-puja is based on scriptural references and the Gaudiya Vaisnava calander. The other information is based on local traditions and needs furthur research.
Ganga personally appeared to Maharaj Bhagiratha before the river descended from Brahmaloka onto Lord Siva's head. Ganga then descended onto the Himalayas prior to Jahnu Rsi swallowing the river. Later, Jahnu released Ganga, which marks the river's reappearance. Afterwards, Ganga descended to Rasatala, liberating the sixty thousand sons of Sagara. Then Ganga appears as Bhogavati in the netherworlds before appearing as Vaitrani encircling Pitrloka.
Ganga-devi appears in her unlimited pastimes for the pleasure of the devotees. Regardless which day one accepts as the appearance day of Ganga, or the day the river descended onto this planet, mother Ganga's pastimes are always appearing throughout the three worlds. Jai Ganga-Mayi!