Lord Ganesha – the son of Lord Shiva and Goddess Parvathi had a weakness for sweets. He could not stop himself from taking the sweets, whenever anyone offered it to him. Once Lord Ganesha's devotee offered him lots of sweets. Lord Ganesha was so pleased that he stayed there the entire day and ate most of the sweets.
After night had come, Lord Ganesha gathering all the remaining sweets, walked home slowly. He had eaten too much and his stomach was full. As Lord Ganesha was walking back he stumbled and fell down. All the sweets scattered everywhere and his dress was torn.
Lord Ganesha was feeling embarrassed as he picked himself up. He dusted himself and collected all his sweets. He looked around hoping no one had seen him. Unfortunately the Moon – Chandra Deva had seen everything.
Those were the days when the moon was full all through the month. There was no such thing as a waxing and waning period of the moon.
Seeing the pot bellied Ganesha stumble and fall, Chandra Deva fell about laughing hard. Chandra Deva thought of himself as very handsome. He always thought that the pot bellied Ganesha with his stumpy feet and elephant head looked funny...He wiped tears from his face as he watched Lord Ganesha pick himself up.
Lord Ganesha was annoyed when he saw Chandra Deva laughing at him. He does not even come and help me...Just laughs at me...
'Chandra!' Lord Ganesha bellowed angrily as Chandra Deva stopped laughing. 'You laughed at me! You think you are so handsome! I curse you that henceforth you will disappear from the sky and never show your face again.
That stopped Chandra Deva cold. Oh God! Now no one would be able to see me...Chandra Deva shook his head The punishment was too harsh...
Chandra Deva immediately came up to Lord Ganesha. 'Lord! Please forgive me! I was proud! I am sorry...Please! Chandra Deva begged the Lord
Lord Ganesha looked at Chandra and realised that Chandra's pride had been broken. Lord Ganesha is always quick to forgive. He smiled and nodded his head. But Lord Ganesha realised that he could not take back his curse.
'Chandra, I cannot take back my words' Lord Ganesha saw Chandra Deva droop and look unhappy, looking at him desparately, 'But listen Chandra, I will lessen your curse. You will slowly reduce in your appearance and there will be only one day when there will be no moon in the sky and on the days following the new moon day, you will keep increasing in size and finally glow on the fifteenth day in your full size...'
Chandra nodded his head happily, 'Thank you Lord!'
Lord Ganesha thought of something and said with twinkling eyes, 'There is one more thing!'
Chandra looked at Lord Ganesha scared that there would be some other condition. Lord Ganesha shook his head, 'No nothing like that! You laughed at me on the Chaturthi. Whoever sees you on this day, would have some problems...However do not worry, these problems would be solved if you listen to the story of Krishna and the Syamantaka Gem'
It was from that day onwards that the moon has been decreasing in size before the no moon day and increasing till the full moon day!
The story of Krishna and Syamantaka Gem is another story.