Among the different aspects of Ganesha Chaturthi, there is a saying that on this day, one should not see the moon, else one will face false allegations in the coming year. The story also provides a solution as to how one can redeem oneself of that ‘curse’.

Among the different aspects of Ganesha Chaturthi, there is a saying that on this day, one should not see the moon, else one will face false allegations in the coming year. The story also provides a solution as to how one can redeem oneself of that ‘curse’.
On the 4th day of the Bhadrapad month, Lord Ganesha was returning to his abode on his vehicle, the mouse. He had been fed well by his devotees. Seeing this sight of the huge Lord on a tiny mouse, the moon in the sky began to laugh aloud. He was vain about his splendor and beauty and thus he laughed. Little did he know that all his splendor was only a ‘reflection’ of the Sun God. In order to teach the vain moon a lesson, Lord Ganesha cursed that no light ever fall on him again. Thus, the moon had no light and disappeared from the skies.”
“Be it the moon or any other being, if he/she forgets that source, they get plunged into the darkness of ignorance." The moon repented and sought pardon from Lord Ganesha. All the other beings of the world too pleaded on his behalf to Ganesha and the Lord acceded. However, once a curse is pronounced, it cannot be taken back, even by God. ‪ It can only be modified. Thus we are advised to be careful about our speech in everyday life. Lord Ganesha modified the curse and said that the moon would undergo regular waxing and waning to remind him to be humble. He also added that anyone seeing him on the 4th day (Chaturthi) of the Bhadrapada month would face blame and unjust criticism.”
The story further goes to say that even Lord Krishna had to bear this curse as he too was accused of stealing the jewel “syamantak Mani(pearl)” because of looking at the moon on the day of ganesh chaturthi.

Say if you happen to see the moon by mistake on that day, what do we do now?
1. see the moon on 3rd and 5th day as well which is the day before and he day after the day of Ganesh Chaturthi.
2. Read or listen to the episode that describes the theft of syamantak mani as narrated in chapters 56 and 57 of tenth skanda of Shrimad Bhagwatam.
3. recite the following mantra that with a glass of water in your hand and then drink that water.

"सिन्ह प्रसेनमवधीत् सिन्हो जाम्बवता हतः |

सुकुमारक मा रोदीस्तव ह्येष स्यमन्तकः ||"
"Sinha prasenamavadheet sinho jaambavataa Hatah
Sukumarak maa rodistava hyesha syamantaka"
Meaning: O handsome prince, it is for this pearl that Sinha killed prasena and Jaambvan killed the sinha, so please do not be upset. Now you and only you have the right to this pearl.

So here’s hoping you don’t see the moon on the day of ganesh chaturthi, but just in case, then do theses remedies to get rid of the ill effects of the sight.! Jai Shri Ganesha!