The Vedic seers and thinkers composed hymns to eulogize light and darkness and they conceived of Usha and Ratri as two goddesses and used to worship them. They ascribed godhood to the Sun, the Thunder, the Fire, the Air, the Water, the Clouds etc. and called the Sun as Aditya, Lord of thunders as Indra, the lord of fire as Agni, the lord of Air as Bayu, lord of water as Baru, the gods of clouds as Marut etc. The rishis of the Rg Veda looked upon the universe in three spheres mely, Dyuloka (celestial sphere), Antariksaloka (the intermediary sphere) and Bhuloka (the terrestrial sphere). Earth ( Pritvi) is the Bhuloka. Visnu, one of the Adityas is the highest God per excellence which is applied to no other god in the Rg Veda. However, in the Vedas, Indra is mentioned in all the Vedas and the prominence of Visnu was fully developed in post-Vedic period and particularly in the Puras and in the epics.