In Hinduism, Vritta is an imaginary closed curve drawn on the celestial sphere. The vritta is imagined to facilitate the study of celestial events, locations and planetary positions. Most of the vrittas are great circles. Important among them are the following –
Vishuva Vritta – equator – dividing the globe equally into two parts and 90 degrees from each pole.
Kranti Vritta – ecliptic – an imaginary path of sun, making an angle of 23.58 with equator.
Purvapara Vritta – a prime vertical passing through east and west ends of equator.
Kshitija Vritta – horizon – separating the sky and earth.
Yamyottara Vritta – meridian – any great circle through both poles.
Vedhvalay Vritta – vertical circle.
Ahoratra Vritta – any circle parallel to equator
Krantimapak Vritta – declination circle
Sara Vritta – measuring celestial latitude
Natonnatansh Vritta – a vertical circle through zenith
Unnatansh Vritta – for measuring an altitude of an object.
Driksep Vritta – a vertical circle passing through the zenith perpendicular to horizon
Vikshepa Vritta – orbit of moon
Kaksha Vritta – orbit of a planet
Akshamsha Vritta – a great circle for measurement of latitude
Karka Vritta – tropic of cancer – a circle parallel to and in the north of the equator at 23.5 degrees.
Makara Vritta – tropic of Capricorn – parallel to and in the south of equator at 23.5 degrees. Karka and Makara vritta together are called Ayan Vritta.
Rekhamsha Vritta – a great circle for measurement of longitude.
Natakalamsha Vritta – for finding an hour angle.
Dhruvsampat – Prot Vritta – equinoxial collier
There are some other vrittas of reference, like Bhuyamyottara, Bhumadhyarekha, Lamba, Laghu, Maha, and Uupa Vrittas.