Discernment of the Truth of Astronomical Principles

The following section discusses the visual obstruction caused by the Earth's curvature and the resulting calculations for planetary visibility.

On the Visibility of the Planetary Spheres

Because of the Earth's surface, the sight of a person is obstructed in certain directions. Above the Earth, the vision of the observer is cut off; as much as the sphere of the Earth moves forward, that same amount is obscured in the planetary sphere. Within that own sphere, the moving celestial body is seen by men. When the sight of the Earth and the sight of the planet meet in the sky, the rising and setting of the planet occurs.

Therefore, the wise astronomer should know that everything regarding the rising and setting of planets, such as the Moon, is established through the geometry of these spheres. Just as the Earth does not move through the planetary spheres by touch, the movement and the speed of the rising and setting are spoken of by the people. The Earth's disk is perceived within the blue sphere original: nīlo-vari-golaka; likely referring to the blue sky or the atmosphere according to its form.

Because of the difference in height—being high or low—the rising of the sun and planets in the sky appears different. Depending on where the observer resides on the Earth, the vision is cut off at different points. Because of the rotation of the planets and the specific position of the observer on the Earth's surface, the rising and setting are perceived differently. This is caused by the difference in the observer's line of sight.

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Due to the wondrous nature of the Earth's position and the observer's sight, the state of the planets is determined in mathematical calculations. By this method, the wise determine the minute discrepancies truṭi|a very small unit of time or a slight observational error for the sake of establishing the exact time of planetary visibility.

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The Sphere of Air and Atmospheric Phenomena

Above the sphere of the Earth original: ku-golād, there is the air vāyu|the element of wind or the atmosphere, which is consistently cold. Above this, it is said by some that the rising and setting of the celestial bodies are affected by the nature of the vapors. Just as fire produces vapor, so too does the air produce upward-moving vapors. These vapors, dark like the skin of a deer, travel through the sky for many years.

It is said that the planets move through these layers with great speed. Similarly, the falling of sun-rays, the appearance of lightning, and the wondrous City of the Gandharvas original: gandharvapura; a traditional term for a mirage or fata morgana occurring in the atmosphere are explained by these atmospheric conditions. Comets ketavo|meteors or comets, which are seen as givers of omens or results, also exist in this world.

These phenomena—great diseases and atmospheric changes—are all caused by the interaction of these vapors with the heat and light of the sun-rays. Below the celestial bodies, these vapors are situated. External colors and scents original: gandhaka; literally sulfur or fragrant substances, here referring to atmospheric particles go everywhere from the Earth due to the combination of these vapors. According to the science of fire original: agni-śāstra; possibly referring to thermodynamics or the study of light and heat, stars and other celestial bodies are observed within their spheres.

Similarly, through the application of cold or by the force of the wind, stones that are hard and firm original: pāṣāṇaiḥ; referring to meteorites fall from the sky. These stones wander through the atmosphere, driven by the power of the air, until they fall to the Earth.