The most fundamental of Hindu deities, is the Trinity of Brahma, Vishnu and Shiva - popular deities include Ganesha, Krishna, Hanuman and goddesses like Lakshmi, Durga,Saraswati.
Once Ganesha partook of a huge meal of modaka a sweet greatly favoured by him) and was riding home on his vehicle, the mouse. Suddenly the mouse was tripped by a snake. Ganesha fell off his back and his over-full stomach burst open and out tumbled the modaks. Seeing this comic sight, Chandra, the Moon, burst into laughter. Ganesha got up, picked up the snake and tied it around his broken waist-line. (This snake-belt can be seen in many sculptures of Ganesha.He then threw his broken tusk at the Moon and cursed him so that he would never again shine at night nor appear in the heavens. (In those times the full moon shone every day in the yearWithout the Moon, there was no night, no moonlight and no twilight. Young lovers moaned and wailed and the old groaned when they found they could not sleep in the bright sunlight, which now shone even at night. The gods found life in the heavens as intolerable as human beings found the earth without the Moon.The gods rushed to Ganesha and pleaded with him. The kind-hearted Ganesha relented but said that the Moon would no longer shine in full glory every night.He would wax and wane from a bright fortnight to a dark fortnight ending with the Full Moon and the New Moon alternately.Also, it would not be lucky to see the Moon on Ganesh Chaturthi day (the fourth day of the bright fortnight) in the month of Bhaadrapad, as one who does will be the victim of scandal.This superstition exists to this day, and people carefully avoid looking at the moon on Ganesh Chaturthi, the day of the festival of Ganesha. The over-superstitious however look downwards on Chaturthi day or the 4th day of the bright fortnight not only once a year but every month to be on the safe side.