Lord Ganesh visited his Devotee’s houses. He was offered with Modhaka (a Sweet Item). He had it to his heart’s content. His stomach was full. After visiting devotee’s houses, lord ganesh was returning home by mounting on his rat vehicle. When he was on the way to home, at one place the rat observed a snake and got terribly afraid. The rat suddenly stopped moving due to fear. Lord Ganesh lost his balance and fell down on the road. His stomach got opened. He immediately realized the situation. He caught hold of the snake and tied it around his stomach to close it. Moon was watching all this happening and mockingly laughed at Lord Ganesh. Lord Ganesh got angry and cursed Moon to lose his luster. The Moon lost his luster immediately. Lord Ganesh further told that whoever looking at moon on Chathurthi Thithi (waxing moon) in Sravana month, they will become sinners. That is why people do not look at Moon on Ganesh chathurthi day.
The place where the above incident took place was Vrichika Rasi. Vrichika is the sign of reptiles. The place abounded with lot of snakes and Scorpions. Vrichika is the exaltation sign for Kethu and debilitation sign for Moon. The presiding deity for Kethu is Lord Ganesh. This is the Astrological Significance hidden in the above story.