Siddhanta Shiromani (Crown of Treatises)

...it is observed that they are similarly moving in their own paths with an Eastward Motion original: "प्राग्गति" — prāg-gati. From that [rotation], their speed varies.

The Five Forms of Time

The status of the year and the planetary motions are governed by the Five Forms of Time kāla-mūrti. These are dependent on the Orbits bhagaṇa and are the underlying causes of the motion of the planets. We will explain this in great detail in the chapter on the Celestial Sphere gola.

And thus it is stated in the Surya Siddhanta The "Treatise of the Sun," a foundational text of Indian astronomy dating back to at least the 6th century CE.:

"The invisible forms of Time, residing within the orbits, known as the Fast Apex śīghra The conjunction point or the center of the epicycle for inner/outer planets., the Slow Apex manda The apogee, the point where the planet is furthest from Earth and moves slowest., and the Nodes pāta The points where a planet's orbit crosses the ecliptic., are the causes of the planets' motions."

Struck by these forces, the planets are bound by "reins of light" original: "रश्मिभिर्बद्धा" — raśmibhir-baddhā; a poetic description of gravitational or magnetic-like pulls.. They are pulled by these "hands" toward the left and right, moving them toward the East or the West.

Depending on their proximity to these directions, they are drawn along. When they are struck by these cosmic winds, they exhibit various types of motion:

• Retrograde vakra Appearing to move backward against the stars.
• Quasi-retrograde anuvakra
• Deficient vikalā
• Very Slow mandatara

These motions, including the Node-driven sapāta movements, occur because of the pulling force exerted by the Fast Apex śīghrocca. When a planet is situated far from its "Fast" point, the attraction of these "reins" causes the planetary motion to appear retrograde. This is called Retrograde Motion vakra-gati.

Now, for Mars and the other planets, to find the Slow-Corrected Position manda-sphuṭa The planet's longitude after correcting for its elliptical orbit., one must look at the distance from its own Fast Apex. By subtracting the planet's position from its apex, we find the Anomaly kendra The angular distance used to calculate the planet's specific position in its epicycle.. If the Fast Apex is greater than twelve signs...