atha ca yavan nabho-mandalam saha dyav-aprthivyor mandalabhyam kartsnyena sa ha bhuñjita tam kalam samvatsaram parivatsaram idavatsaram anuvatsaram vatsaram iti bhanor mandya-saighrya-sama-gatibhih samamananti.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The sun-god has three speeds — slow, fast and moderate. The time he takes to travel entirely around the spheres of heaven, earth and space at these three speeds is referred to, by learned scholars, by the five names Samvatsara, Parivatsara, Idavatsara, Anuvatsara and Vatsara.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
According to solar astronomical calculations, each year extends six days beyond the calendar year, and according to lunar calculations, each year is six days shorter. Therefore, because of the movements of the sun and moon, there is a difference of twelve days between the solar and lunar years. As the Samvatsara, Parivatsara, Idavatsara, Anuvatsara and Vatsara pass by, two extra months are added within each five years. This makes a sixth samvatsara, but because that samvatsara is extra, the solar system is calculated according to the above five names.