I've been working on a task in the area of astronomy, regarding influence on climate by astronomical factors. However, the work is rather tough and I have a problem on wording of "amplitude of precession". You definitely know about the precession of Earth's axis, once in 25 765 years. It is also called precession of equinoxes, because the Equator and the Ecliptic will intersect at points that are moving against background stars (at some speed). All clear so far. There is another kind of precession that is simply speaking, the rotation of the Earth's orbit once in 112 000 years relative to background stars which doesn't seem to matter much to the climate, because it is all relative and only Sun matters. 1. according to the position of the equinox relative to the Sun on ecliptic we measure tropical year, SEASONS and calendar. 2. according to the position of the equinox relative to the perihelion (closest point to the Sun on orbit) we determine where on the Earth's orbit is the equinox. When we know that, we know what SEASON it is when the Earth is closest to the Sun. The cycle takes 21 000 years to repeat the event of equinox and perihelion happening on the same day. Now I don't know why I had to say all that when it is on the internet, here http://en.wikipedia.org/wiki/Precession_(astronomy) I call this cycle the cycle of climatic precession. According to eccentricity, the orbit may be more elongated or more round like a circle. If it is more elongated, the AMPLITUDE of precession is greater. It is further said that eccentricity modulates precession. You can review this greatly chaotic presentation: http://www.soest.hawaii.edu/GG/FACULTY/POPP/Lecture12.ppt I am trying to find a simple passage of text to properly define the "amplitude of precession". Slides 23, 24, 25... are about that topic. Precession index p = eccentricity sin(omega) somehow includes two kinds of precession. Not clear. Precession index turns precession into sine wave, and eccentricity stands for amplitude. All clear. Precession index is 23 000 years cycle. Not clear. Possible solution: ignore the number and continue. Any ideas? --------------------------------------------------------------- Part II I am using the following statements. The axial tilt and precession for that matter, are not expected to change the GLOBAL insolation because the distance to the Sun is always the same. The tilt says how much sun is there at the poles or at some latitude at what angle. Climatic precession modulates seasonal cycle. http://www.people.fas.harvard.edu/~phuybers/Doc/HuybersThesis.pdf [Broken] Only eccentricity changes GLOBAL insolation because of the different distances at which Earth is passing by Sun. http://en.wikipedia.org/wiki/Milankovitch_cycles However, if we pretend that eccentricity is really high value. Planet could be so far out of sunlight once a year that it would get cooler a lot. Does it take away the heat and returns the ONE YEAR AVERAGE to standard value as for circular orbit? In this question I disregard the nonlinear domain where on some other planet the heat may be stored for long time so it doesn't matter and so on. These are my thoughts, thanks for reading, if you have some idea about precession I would appreciate it.