Ganesh Chaturthi is celebrated on the birthday of Lord Ganesh (Ganesha), the god of wisdom and prosperity on the fourth day of the moons bright fortnight, or period from new moon in the lunar month of Bhadrapada. The celebration of Ganesh Chaturthi continue for five, seven, or ten days. Some even stretch it to twenty one days, but ten the most popularly celebrated. In the tradition of the right hand path the first day is the most important. In the left hand path tradition the final day is most important.
Ganesha is the god of wisdom and prosperity and is invoked before the beginning of any auspicious work by the Hindus. It is believed that for the fulfillment of one's desires, his blessing is absolutely necessary. According to the mythology, he is the son of Shiva and Parvati, brother of Kartikeya - the general of the gods, Lakshmi - the goddess of wealth and Saraswati-the goddess of learning. There are numerous stories in Hindu mythology, associated with the birth of this elephant-headed god, whose vehicle is the Mooshak or rat and who loves Modaks (droplet shaped Indian sweet).
Legend has it that Parvati created Ganesha out of the sandalwood dough that she used for her bath and breathed life into him. Letting him stand guard at the door she went to have her bath. When her husband, Shiva returned, the child who had never seen him stopped him. Shiva severed the head of the child and entered his house. Parvati, learning that her son was dead, was distraught and asked Shiva to revive him. Shiva cut off the head of an elephant and fixed it on the body of Ganesha.
Another tale tells of how one day the Gods decided to choose their leader and a race was to be held between the brothers- Kartikeya and Ganesh. Whoever took three rounds of the earth first would be made the Ganaadhipati or the leader. Kartikeya seated on a peacock as his vehicle, started off for the test. Ganesh was given a rat, which moved swiftly. Ganesh realised that the test was not easy, but he would not disobey his father. He reverently paid obeisance to his parents and went around them three times and thus completed the test before Kartikeya. He said, " my parents pervade the whole universe and going around them, is more than going round the earth." Everybody was pleasantly surprised to hear Ganesha's logic and intelligence and hence he came to be known as the Ganaadhipati or leader, now referred to as Ganpati.
There is also a story behind the symbolic snake, rat and the singular tusk. During one of his birthdays, His mother, Parvati, cooked for him twenty-one types of delicious food and a lot of sweet porridge. Ganesha ate so much that even his big belly could not contain it. Mounting his little mouse, he embarked on his nightly rounds. His mouse suddenly stumbled upon seeing a huge snake. To adjust His belly, Ganesha put the snake on as a belt around his stomach. All of a sudden, he heard laughter emanating form the sky.
He looked up and saw the moon mocking him. Ganesha infuriated, broke off one of his tusks and hurled it at the moon. Parvati, seeing this, immediately cursed the moon that whoever looks at it on Ganesh Chaturthi will be accused of a wrong doing. The symbology behind the mouse and snake and Ganesha's big belly and its relationship to the moon on his birthday is highly philosophic. The whole cosmos is known to be the belly of Ganesha. Parvati is the primordial energy. The seven realms above, seven realms below and seven oceans, are inside the cosmic belly of Ganesha, held together by the cosmic energy (kundalini ) symbolized as a huge snake which Ganesha ties around Him. The mouse is nothing but our ego. Ganesha, using the mouse as a vehicle, exemplifies the need to control our ego. One who has controlled the ego has Ganesha consciousness or God-consciousness.