Varuṇa’s carrier is the fearsome sea-monster called a Makara (“Capricorn”). This, of course, is due to his lordship over the deep seas. But there is something else, extremely interesting here. Varuṇa’s connection with Makara suggests that the ancient positions of solstices and equinoxes may have influenced the concepts of which gods dwell in which stars, and may also serve as evidence that ancient Indians did in fact have a concept of 12 tropical divisions in addition to their unequivocally documented use of sidereal nakṣatra.
The oldest hymns of Ṛg Veda most probably took formal shape at a period in history when the Winter Solstice occurred with the heliacal rising of Śatabhiṣaj. By definition, the Winter Solstice is the beginning of Capricorn Capricorn is called “Makara” in Sanskrit, the creature that Varuṇa travels on.
Varuṇa’s close relationship to the Nāga is also significant here, for in those ancient times the Summer Solstice would have occurred at or very near the heliacal rising of the Nāga’s star, Āśleṣā.
The Summer and Winter Solstices mark the beginning and end of dakṣināyaṇa – the six months the Sun spends below the equator, in the “underworld” of Varuṇa. The entrance and exit from this underworld were guarded by the Nāga and Varuṇa.
The Vernal and Autumnal Equinoxes, on the other hand, occurred in those ancient times with the heliacal rising of Kṛttikā and Anurādhā, respectively. Anurādhā belongs to Mitra, god of the daytime sky – the inseparable polar opposite of Varuṇa, the god of the nighttime sky. Kṛttikā belongs to Agni, the god of fire.
Thus dark underworld gods guarded the solstices marking the entrance and exit to the “southern” half of space, while bright overworld gods empowered the equinoxes.
 Varuṇa is almost always paired with Mitra, but does so with Indra several times in Ṛg Veda. Indra’s star is Jyeṣṭhā, which is right next to Mitra’s Anurādhā.