Ganesha (also called Ganpati) is a Hindu god. The story behind his creation is very interesting. One day godess Parvati; wife of Lord Shiva was applying sandalwood paste (its suppose to be very good for ones skin) before her bath. And with the leftover paste she created a small figure and then decided to breathe life into it. She then asked this young child (who was created from sandlewood putty) to stand guard at the door of the house, while she went for her bath. After a while Shiva returned, while Parvati was still taking her bath. Ganesha didn't know Shiva, so he did not allow him to enter the house. This upset Shiva and he decided to behead the child in a fit of rage and entered his house. But after releasing that he was responsible for his own son's death, Shiva decide to fix the head of the first living being that he found, and this happened to be a baby elephant. And this is why Ganesha has the head of an elephant instead of a human face.
Ganesh Chaturthi festival was not always as big as it is today in Bombay. Its all thanks to a gentleman called Lokmanya Bal Gangadhar Tilak, who wanted to unite lacs of citizens from Maharashtra, by having a common platform which would bind and unite all of them. And he initiated the practice (in 1892) of having Sarvajanic (public) Ganpati and this formed an important aspect of the freedom struggle Tilak used this platform to create and enhance the awareness about the Freedom movement in Mahrashtra. With each successive year the event has grown in stature and size, but over the last decade its become commercial and instead of being a common man's event its been high jacked by sponsor ship money of commercial enterprises and power of local political parties.
History behind the mass participation in Ganesh Chaturthi. This festival unites the entire city, across caste, creed and religion.
I have captured some pictures on my camphone - These pictures are of day one, when the idol is brought to homes & pandals (sarvajanic/public places). The immersion (the idols are immersed in the sea/river/lake) takes place after 1.5, 3, 5, 10 & 11 days.(its staggered over a period of time, the bigger public Ganpati immersions take place after 10 and 11 days, the home Ganpati immersions take place after 1.5 or 3 days)