The Nether-worlds :* Manifestation of the Luminaries - Verse 184-185

Twenty hundreds of Parvans (i.e. a thousand months) constitute a Yuga of the sun. These eighteen plus thirty (i.e. 48) Yugas make one Udaya of the sun. Thirty Rtas of the sun make ten Ayanas. Three thousand five hundred Ayanas make sixty months of the sun.