Krtaveerya’s father once asked Lord Brahma why a Tuesday Chaturthi was special and Lord Brahma began narrating the following story.
There was a Great Maha Rishi , Bharadwaja in the city of Avanti , known for his wisdom and knowledge of the Sashtras. Once while he was having a bath in the river, his eyes set upon a beautiful apsara and he became overcome by lust.
His seed fell unto the Earth, and mingling with the Earth, it became a radiant young boy. This reddish complexioned boy was taken as a Son by the Earth Mother herself who brought him up.
When he grew to be 7 years old and questioned the reason for his birth and red complexion, the Earth Mother brought him to the Ashram of the Great Sage, told the sage of what had transpired and went back to her abode.
Bharadwaja Rishi , hugged his son , and at an appropriate time , initiated him in the Sashtras and the Ganapati Mantra, asking him to take a penance for Lord Ganapati.
The boy, then sat on the rivers of Narmada River, and undertook a penance of a thousand years, never seen before , surviving only on air alone.
Finally, one day the Great God , Maha Ganapati, appeared before him , on a Chathurti tithi, in blazing glory, celestial garments , the moon on his forehead , with the effulgence of a Million Suns.
The boy, known as Bhauma ( born of Earth ) , paid his respected to the Great Lord, singing his praises and pleased , Ganapati asked him what boon he would like.
The boy replied, oh great lord, your appearance today has made my eyes auspicious, my voice auspicious, it has made my family line auspicious , it has made the very earth auspicious, and this very day and tithi auspicious.
If you are pleased oh lord, I desire to be in heaven permanently, to be allowed to drink the divine soma meant for the devas, and may my name become famous across the 3 worlds.
You gave me your divine darshan on this Chaturthi tithi , may this tithi also give merit to anyone who performs a Vrata on this tithi and dissolve their troubles.
Lord Maha Ganapati replied, Bhauma, son of the Earth , you will be with the Devas and drink ambrosia. You will be called auspicious in the 3 worlds by the name Mangala. Because of your red complexion , you will be known as Angaraka.
Those who perform the Angaraka Chathurthi Vrata ( Chaturthi Tithi that falls on a Tuesday ) will have their obstacles dissolved, and the merits will last one whole year.
It will also become known as Mangala ( auspicious ) Chaturthi which confers limitless benefits and as famous as Chintamani, the sacred gem that fulfills all desires.
– Excerpt from The Ganesa Purana ( thanks to a Ganesha Sadhaka for sharing and reminding me of this story that i had read before some years back )
– Shri Maha Ganapataye Namaha , Sangili Karuppar Thunai
– Senthil Shree Kumar