Trayodashi

The thirteenth lunar day (trayodashi) is the day on which Brahma appeased Dharma, the god of righteousness. (Dharma is identified with Yama, the god of death.)

As Brahma sat and thought about creation, the god Dharma was born from his right side. He was fair, had four feet, three horns and was in the form of a bull. (He is also supposed to have had seven hands and two heads.) Brahma decreed that Dharma’s duty would be to check that the humans stuck to the righteous path. As men became evil, Dharma would lose one of his feet. That is, in satya yuga, he would have four feet. But in treta yuga, the number of feet would be reduced to three; in dvapara yuga, to two; and in kali yuga, to one. Dharma would pay brahmanas complete attention, but kshatriyas would only receive three-quarters of Dharma’s attention. Similarly, vaishyas would only receive half of his attention and shudras only a quarter.

The moon-god, Chandra, was Dharma’s brother. (Dharma was Brahma’s son and so was the sage Atri. The Puranas normally state that Chandra was Atri’s son. Thus, as per the other Puranas, Chandra could not have been Dharma’s brother.)Chandra once cast evil looks at Brihaspati’s wife. (Other Puranas state that Chandra abducted Brihaspati’s wife, Tara.) Scandalised at his brother’s shameful act, Dharma left for the forest in disgust. Lawlessness and evil prevailed everywhere on earth as the god of righteousness had gone away. Finally, on trayodashi tithi, Brahma appeased Dharma and brought him back.