The fourth foot (प॒रो-र॑जसे॒ ऽसाव॒द् ओ३म् ॥) of the Sāvitrī implies that Savitṛ shines from beyond the rajas. What is this rajas, or more precisely the rajāmsi, since the Veda knows of a plurality of them. Vāmadeva Gautama says:
While there is a clear emphasis on the tripartation in this mantra, the multiplicity of realms of the old Hindu cosmography is evident here. The rajāmsi are clearly distinct from the atmospheric realm (antarikṣa) and the realms of light (rocana).
The rajas realms are also mentioned as being precisely measured out by the strides of Viṣṇu (e.g. RV 6.49.13; 1.154.1) and are again described as being 3 in number in this context (e.g. RV 6.49.13 ).
In the sūkta of Śyāvaśva Ātreya (RV 5.81) it becomes clear that Savitṛ performs a similar function of mensuration of these realms. One may say that this function of Viṣṇu goes back to the beginning of cosmic time, while that of Savitṛ apparently happens on a daily basis.(5)
Indeed, the two deities are offered combined oblations in the Pratha-Sapratha offerings related to the super-heated gharma pot of the old Pravargya ritual (RV 10.181).
From these references, we can infer that the old ārya-s saw the earthly realm as surrounded by the antarikṣa-s i.e. the atmospheric realms, followed by the rajāmsi “near space”, and then the still more distant celestial realms, the rocana-s and div-s.
The light of the sun was seen as coming from beyond the rajāmsi and Savitṛ is explicitly associated with this light. Thus, the sun may be seen as marking the beginning of the rocana realms (see also RV 10.189.2) or those of light, which include the realms of the stars.
The div-s are seen as three too. Of them two are explicitly described as being under Savitṛ (upastha) while one belongs to the death-dealing Yama (RV 1.35.6). The sun is alluded as being in one of these div-s.
In RV 1.35.9 is stated that the div is reached via the black rajas realms. These allusions suggest that the rocana-s and the div-s are essentially equivalent.
In conclusion, it might be mentioned that the Vedic cosmography was rather elaborate and has been poorly understood due to the assumption that it might have been unsophisticated (barring Lokamanya Tilak’s musings in this regard).