Ritu means Season and Charya means moving or following. Ritucharya is the observance of diet and regimen according to the seasonal changes. In Ayurveda, a year is divided into 2 kaala or periods based on the apparent position of the sun in the north and southern directions. They are

Uttaraayana - north andDakshinaayana - south

Ayana means journeying. Uttaraayana is also called Aadaana kaala or the taking away period. The sun and wind are powerful during this period. The sun takes away the energy of the people. Due to the heat, air becomes hot and drains the cooling effect of earth. Due to this, people get dehydrated and weakened and the atmosphere becomes hot and dry.

Dakshinaayana is also called Visarga kaala or the giving away period. The moon becomes powerful during this period. The sun releases its energy to the people, the earth cools down due to cold winds and rain. People regain their strength and nourishment that was lost in the Aadaana kaala.

Each year consists of six Ritus or seasons. Each Ritu comprises two Maasas or months and three such ritus constitute one kaala. Hence Aadaana and Visarga kaalas each consist of six months and three ritus.