SB 5.22.7

atha ca yāvan nabho-maṇḍalaṁ saha dyāv-āpṛthivyor maṇḍalābhyāṁ kārtsnyena sa ha bhuñjīta taṁ kālaṁ saṁvatsaraṁ parivatsaram iḍāvatsaram anuvatsaraṁ vatsaram iti bhānor māndya-śaighrya-sama-gatibhiḥ samāmananti.
Synonyms: 
atha — now; ca — also; yāvat — as long as; nabhaḥ-maṇḍalam — outer space, between the upper and lower world; saha — along with; dyau — of the upper world; āpṛthivyoḥ — of the lower world; maṇḍalābhyām — the spheres; kārtsnyena — entirely; saḥ — he; ha — indeed; bhuñjīta — may pass through; tam — that; kālam — time; saṁvatsaram — Saṁvatsara; parivatsaram — Parivatsara; iḍāvatsaram — Iḍāvatsara; anuvatsaram — Anuvatsara; vatsaram — Vatsara; iti — thus; bhānoḥ — of the sun; māndya — slow; śaighrya — speedy; sama — and equal; gatibhiḥ — by the speeds; samāmananti — the experienced scholars describe.
Translation: 
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 Saṁvatsara, Parivatsara, Iḍāvatsara, Anuvatsara and Vatsara.
Purport: 

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 Saṁvatsara, Parivatsara, Iḍāvatsara, Anuvatsara and Vatsara pass by, two extra months are added within each five years. This makes a sixth saṁvatsara, but because that saṁvatsara is extra, the solar system is calculated according to the above five names.