Ancient Siddhaanta and Phalit classics mention eight types of speeds (Gati) of planets. All these eight types apply to Pancha-taaraa planets only : Mercury, Venus, Mars, Jupiter and Saturn. Rahu and Ketu are always retrograde. Sun and Moon are never retrograde.
The eight types of speeds are as follows :-
- Vakra (Faster Retrograde)
- Anuvakra (Slower Retrograde)
- Kutila (complicated and very slow retrograde, sometimes relapsing into non-retro)
- Mandatara (slowest forward motion)
- Manda (slow forward motion)
- Sama (normal forward motion)
- Sheeghra (fast forward)
- Sheeghratara (very fast forward)
These eight speeds according to their numbers are shown in the picture below, which is GEOCENTRIC epicycloidal motion of any Pancha-taara planet. In heliocentric model, there is no such differentiation and speed is always "sama". In Geocentric system too, speed of Sun or Moon is always "sama".