2
$\begingroup$

Unless there's a twin star to our sun in which case axial precession might be an illusion the Earth's wobble won't effect the total amount of energy received from the sun as is expected from increased ellipticity, but will effect the amount of sun's energy to the Northern and Southern hemispheres in a cyclical 26000 (and diminishing) year period with periodic further exacerbations caused by variations in tilt.

How has Precession and variations in tilt been factored into the weather change model if at all?

As a side question: On the Salisbury Plain 6500 yrs ago according to wobble theory the East-West alignment going by the apparent motion of the sun across the sky must have been different to today. Can anyone tell me how to calculate the difference in respect to Grid North please?

Background:
I'm building a picture of Neolithic Britain and want to know the orientation of East-West in this time period to check for orientation practices if any. The particular time period I'm interested in lies about half way along the Axial Precession's swing so I'm interested to know A) Whether the axial precession exists or not and B) How the theory is in agreement with the weather patterns for the last 24000 yrs on Salisbury Plain.

Improve this question
$\endgroup$
5
  • 1
    $\begingroup$ Instead of adding a comment you can edit your post to make it better. Comments may disappear. After that, delete your comment. $\endgroup$
    – Jan Doggen
    Jan 1, 2016 at 12:48
  • $\begingroup$ Axial precession doesn't change the amount of the north pole's tilt, just its direction. The sun still follows the same pattern across the sky, just at different times of the year (depending on how you define 'year'). $\endgroup$
    – user967
    Jan 8, 2016 at 16:36
  • $\begingroup$ Re the side question : I think there is astronomy software available that allows you to calculate the positions of celestial objects at arbitrary dates. Some of this may be cheap or free, and may include axial precession - so if this is the case, you could just wind it back the right number of years and see where the sun is. $\endgroup$
    – Semidiurnal Simon
    Jan 9, 2016 at 8:53
  • $\begingroup$ Simon W - Thanks. Stellarium is free and Starry Night Pro (Payware) has been recommended too. The sun is always East by definition. The affect of Precession means the plane of our tilt returns to a point in the direction of a sun's merridian 20 minutes per year earlier than a full cycle which means along with the extra day every four years added due to the additional quarter day in our yearly cycle we also have to add an extra day every 72 years. The question is do we really have a wobble since the planet doesn't apparently rotate about the x axis or are we in a vortex chasing the sun? $\endgroup$
    – Miles Smiles
    Jan 10, 2016 at 10:30
  • $\begingroup$ Barry Carter - Thanks.The planet rotates faster or slower than ideal, and, completes its cycle of the sun quicker than expcted. With no addition or subtraction to the tilt cause by precession along the y axis of the 'wobble' and no rotation about the x axis by definition (the sun is always in the east at the equinox) can it be truly called a wobble? Perhaps the sun has a wobble in its movement through space? The earth does nod and cause the tilt to increase and that must affect the weather over time. 6500 yrs ago everyone lived on hills cause valleys were too wet? Are we heading towards that? $\endgroup$
    – Miles Smiles
    Jan 10, 2016 at 11:02

1 Answer 1

Reset to default
1
$\begingroup$

You may be better off getting a more precise answer by cross-posting this physics if you want a precise mathematical explanation of the model.

First, axial precession, as mentioned above, is different than axial tilt. Both change over time, but on different time scales.

That said, the answer is it has most certainly been explored: Milankovitch cycles are an attempt to explain patterns of solar forcing on climate. The wikipedia article does a fairly good job of laying out the foundation of the theory, which is that there are three key components influencing solar forcing: eccentricity (how elliptical our orbit is), axial tilt (the change in amount of tilt of the earth), and axial precession (the actual change of direction of the poles). All three components operate on different time cycles.

Unfortunately for us, the nice Milankovitch theory leads to a huge conundrum: the predictions don't play out as expected. Physics dictates that eccentricity would have the weakest effect of the three, but the largest fluctuations are seen in roughly 100ky intervals (tilt and precession operate on roughly 25k and 50k intervals, eccentricity roughly 100k). This leads to the 100,000 year problem.

Now, all of this is in the context of climate on the global scale, but the point applies just as well: nobody has a conclusive answer as to what exactly is going on, hence the entire field of paleoclimate. Unfortunately for scientists, the Earth is far from a simple rock: our physical (ocean, atmosphere) and biological systems are so complex that it is often too simplistic to pin down changes on one particular phenomenon on a geological time scale. People can study the temperatures of individual sites over time, but determining the big picture cause of those fluctuations is tough enough for the planet as a whole, much less for a location as specific as the Salisbury Plain.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Bill Harper - Amen to that. Still 10000 yr cycle for ice ages means we in the north will want to move south at some point. What geopolitical nightmare are we creating for ourselves in the mean time creating borders and fighting to eradicate nomadic life styles ? $\endgroup$
    – Miles Smiles
    Jan 10, 2016 at 11:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.