In the Vedic tradition, Agastya is one of the Saptarishis — the seven great sages whose names are given to the seven stars of the Ursa Major constellation (Saptarishi Mandal). He is the author of several hymns in the Rigveda and is considered among the earliest of the great rishis.

In the Puranic and epic tradition, two of his stories stand out. The first: the Vindhya mountains, in a contest of height with the Himalayas, kept growing until they began to block the path of the Sun. No one could stop them — the mountains refused to bow to any god. But they respected Agastya. When the sage arrived from the north on his way to the south, the Vindhyas bowed low to let him pass, as a mark of respect. Agastya told them to stay bowed until he returned — and then never came back from the south. The mountains are still waiting. This is why the Vindhya range never grows to the height of the Himalayas.

The second story: a group of demons called the Kalakeyas hid in the ocean to escape the gods, emerging only at night to attack sages and sacred sites. The gods couldn't reach them because the ocean was too vast and too deep. Agastya drank the entire ocean — emptying it completely — so the demons had nowhere to hide. The gods killed them. Then Agastya could not restore the ocean, which remained empty until Bhagiratha's long austerities eventually brought the Ganga down from the heavens to fill it again.

In the Tamil tradition, Agastya occupies an even more central place. He is credited with creating the first grammar of the Tamil language — the Agattiyam — making him the founding figure of Tamil literary culture. He is revered in the south as Agathiyar, a siddha (enlightened master) who is said to still be alive, meditating in the Pothigai hills of the Western Ghats. His connection to both the Sanskrit north and the Tamil south makes him one of the few figures who genuinely bridges those two worlds.

During the summer monsoon months (roughly June through August), Canopus is lost in the glare of the sun and invisible. When it reappears in the southern sky in late August or September — its heliacal rising — ancient astronomers noted it as a reliable seasonal marker. The timing corresponded with the monsoon's withdrawal. Rivers were clearing. The heavy rains were ending. Canopus returning was the sky's announcement that the difficult season was over.

In the Bengali panjika, the exact date of Agastya Uday is calculated based on this astronomical event. In 2026, it falls on September 4. The puja is performed facing south — the direction of the star and of Agastya's mythological home — at either dawn or dusk, when the star is visible.