From your link: "The year – starting with Makara Sankranti, the sun's entrance into Capricorn – is divided into two halves and six seasons."
In the time of Vedas, an year was divided in five seasons: Vasant (Spring), Greeshma (Summer), Varsha (Rains), Hemant (Autumn), and Sharada (Winter). This was followed by a long, cold, dark Arctic night which extended for two months. There was no sixth season. When the Aryans moved South because of the ice-age, a sixth season Shishir (Colder than winter, snow) was added to the calender.
"Pańcapādam pitaram dvādashākritim diva āhuh pare ardhe purīshinam;"
(They call him in the farther half of heaven the Sire five-footed, of twelve forms, * wealthy in watery store.)
Rig Veda: Rig-Veda Book 1: HYMN CLXIV. Viśvedevas.
, Verse 12
* Wealthy in watery Store: The Aryans meant 'life' when they said 'water' (apah, that was one of their Gods), because water gave life to vegetation and grass for their live-stock. During the Arctic night, all things were frozen. Aryans longed for the sun and water (through their sacred celestial river, Sarasvati) to appear again so that their live-stock could graze and they could lead normal life.