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A Milancovitch cycles and how they relate to seasons

  1. Nov 17, 2017 #1
    There are 3 cycles important for determining seasons, extreme temperatures, and length for any given planet in any given orbit as long as it isn't too elliptical.

    Those are:
    • Orbital precession(this is what causes supermoons(when perigee lines up with a full moon))
    • Axial tilt(this determines the extremes of seasons and whether or not there are seasons)
    • Axial precession(change in axial tilt over thousands of years)
    Eccentricity is important but only in the case of the orbit being so elliptical it actually changes zones as it orbits. For example, if eccentricity is close to 1, Summer would correspond to being in the hot zone and would be very short, Winter would correspond to being in the cold zone and would be very long(like maybe hundreds or thousands of years long. Spring and Fall would correspond to being in the habitable zone and have a length in between that of Summer and that of Winter.

    But assuming eccentricity is only a factor in that it determines orbital precession and is not so high that the planet is in different zones at different points in its orbit, how would I calculate the orbital precession and the axial precession of any planet around any star where the planet's eccentricity is not too extreme?
     
  2. jcsd
  3. Nov 17, 2017 #2

    phyzguy

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    Science Advisor

    The attached excellent paper, which I've cited several times on this forum, looked at exactly that question by simulating the occurrence of Ice Ages with each of these factors turned off. Their conclusion was as follows:

    "To understand the relative importance of the three astronomical
    parameters in generating the,100-kyr cycles of the North American
    ice sheet, we conducted model experiments in which we kept fixed the
    eccentricity, obliquity or precession in turn, under a constant CO2
    concentration of 220 p.p.m. Results show that the ,100-kyr cycles
    persist for fixed obliquity, but not for fixed eccentricity or for fixed
    precession (Fig. 3 and Supplementary Fig. 6). These results demon-
    strate the essential role of precession and the eccentricity variation for
    the,100-kyr cycle. Obliquity is not the driver of the ,100-kyr cycle,
    although it helps to amplify the ice-volume changes from glacial states
    to interglacial states. In summary, our model results suggest that the
    ,100-kyr cycle is essentially produced by the eccentricity modulation
    of precession amplitude through the changes in summer insolation"
     

    Attached Files:

  4. Nov 17, 2017 #3

    jim mcnamara

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    Staff: Mentor

    Okay @caters. You got a grade 'A' answer. My suspicion is that you would have trouble implementing what you asked for on that level. So what do you think we should try? Orbits involve some interesting math. How many semesters of calculus have you completed? If you think paper this is for you, go to the bottom of the link and find how to get the full methods for the simulations. Exactly what I believe you asked for.

    We are here to help....
     
  5. Nov 18, 2017 #4
    I have completed almost 3/4 a semester of calculus(half of the semester was about derivatives and I am about halfway through doing integrals). I haven't done calculus with multiple variables other than implicit differentiation(which is a way to get a 2 variable equation to a 1 variable derivative). I have started studying General Relativity. I know Newtonian Physics very well.
     
  6. Nov 18, 2017 #5

    jim mcnamara

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    Staff: Mentor

    Okay. Let's see what we can do. You realize that I do know what you are good/bad at in programming - python is simple and has wonderful libraries of code that do the heavy lifting.

    http://fiftyexamples.readthedocs.io/en/latest/gravity.html

    This has python code. If you do not know, python is freely available for Windows and Linux.
    So go here: python software foundation - https://www.python.org/downloads/windows/

    If you need help setting up and running, just jump over to the programming forum and ask for help.

    The code attempts to model the earth's orbit accounting for external parameters. There are other examples on that site.
     
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