The path of grahas are seen with respect to earths' motion in Jyotish. So it's important to understand various movements of earth. Here is an interesting article on, http://en.wikipedia.org/wiki/Milankovitch_cycles
- Orbital Shape: The earth rotates around sun from nearly Circular shape to elliptical shape. This changes periodically.
- Periodicity: 413,000 years
- Reason: The Earth's eccentricity varies primarily due to interactions with the gravitational fields of Jupiter and Saturn.
- Axial tilt : The axis of the earth is currently inclined at 23.44 degrees. But, This angle changes periodically from 22.1 to 24.5 degrees.
- Periodicity : approximately 40,000 years
- Reason : Not Available.
- Axial orientation : The Tilted axis of the earth, rotates around. If you imagine an non-tilted axis thru center, then the actual tilted axis rotates around it.
- Periodicity : roughly 26,000 years
- Reason : This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the solid Earth.
- Orbital inclination : The earth rotates around the sun on an imaginary plane. This plane tilts periodically. The Plane of Jupiter is considered as invariable. So declinations with respect to Jupiter's path will give variations.