Gola, or sphere, has played an important role in the development of Hindu astronomy down the ages. In Hinduism, spherical trigonometry has been employed for the explanation and elaboration of astronomical phenomena, computation of planetary longitudes and for solving problems.
Three basic spheres are conceived by Hindu astronomers –
- bhugola (earth sphere),
- vayugola (atmosphere sphere) and
- akshagola or bhagola (zodiacal sphere).
Vayugola is taken as one having in its periphery the three great circles, the ghatikavitta (celestial equator), the dashinottaravritta (celestial meridian) and the lanka kshitija (the east-west great circle passing through lank and touching the two poles.
Bhagola or akshagola is conceived as being encircled by the zodiac, the apakrama mandala (ecliptic circle), the ghatika-mandala (celestial equator), the motion of the sun and the moon, the equinoxes and solstices.
It is also demonstrated how the conception of the three spheres and the attendant great circles facilitate planetary computation and the elucidation of related astronomical phenomena.
Gola is discussed in many Hindu astronomical texts.
Full-fledged treatises on Gola are found in the works of Vateshwara (880 AD) titled Gola, the Goladipika or Golanyayadipika. Another important work is the Golasara of Parameshwara (14th – 15th century). Other texts include anonymous works titled Golakatattva, Golattatvanirnaya and Golarachana.