Rayee and prana are conceptual pairs. Prajapathi alone comes as conceptual pairs of rayee and prana.
Samvatsara, consisting of dakshinayana and utharayana (kala) is prajapathhi.
Krishna kathi and chukla kathi are subtle or divine road through which a jiva travels to other logas. Krishna kathi leads to Chandra loga and chukla kathi leads surya loga or brahma loga. Those people who perform rituals go to Chandra kathi and those who perform upsaha will go to surya loga. Gyani does not go through either of the logas because he gets moksha here and now. Dhashinayanam represents Krishna kathi and represented by various dhashinayana devadas; utharayanam represents chukla kathi presided by utharayana devadas.
Krishna gathi, dakshinayanam and Chandra loga are all rayee; Utharayanam, surya loka and chukla gathi are all prana.
Chukla kathi is the path; the travelers are upasaha or karma upasa samuchayaha. Brahama loga is immortality because brahmaloga gives moksha which is immortality. Upasaha seek surya loga, upasana by following discipline (control of sense organs and faith in scriptures). For all pranas, this surya loga is the goal. This loga is mean for upsahas only and not available to others.
Adhithya praised as a destination of chukla gathi: Surya is endowed with five feet (five seasons are taken as feet of Surya loga because Surya moves creating the five seasons) so surya is called panca patham. Six seasons in scriptures are spring, summer, rainy, autum, pre-winter and winter. In this verse pre-winter and winter are combined as one season. There are 12 different appearance to sun one for each month. Due to utharayanam and dakshinayanam, sun is the father of all beings.