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Altering the Milankovitch Cycles

  1. Dec 11, 2015 #1
    As I understand it, the Pleistocene ice ages were dictated by three major factors suggested by the Serbian geophysicist Milutin Milankovitch--eccentricity (orbital shape), obliquity (axial tilt) and precession (direction of rotation in relation to fixed stars).

    The one identical factor between our Earth and this alternate Earth is the eccentricity--no lower than 0.000055 and no higher than 0.0679.

    Back home, Earth's axial tilt varies between 22.1 and 24.5 degrees in a period of 41,000 years. In this alternate Earth, the tilt varies between 20 and 25 degrees in a period of 61,500 years.

    Back home, Polaris will be the North Star for a total length of roughly 26,000 years. In this alternate Earth, Sirius will be the North Star for a total length of 46,800 years.

    With these changes, how much dramatic of a difference would Earth's climate be? How would they affect the extents of the ice ages?
     
  2. jcsd
  3. Dec 11, 2015 #2

    tony873004

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    Polaris will not be the pole star for 26,000 years. It becomes the pole star for a few hundred years every 26,000 years. It has been doing this, and will continue doing this until its proper motion takes it significantly far from its current location
     
  4. Dec 11, 2015 #3

    fresh_42

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    Did you mean Sirius or is Wiki wrong here?
    https://en.wikipedia.org/wiki/Polaris
     
  5. Dec 12, 2015 #4

    tony873004

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    Polaris is currently the pole star. In a few hundred years, it will not be as close to the pole. In 26,000 years it will return to the pole position. During every 26,000 year period, several stars take turn being the Pole star, including Vega.

    Sirius can never be the north star as it is in the southern sky.
    With a tilt of 20-25 degrees, it can't ever be the southern star either. It is too close to the celestial equator.
     
  6. Dec 12, 2015 #5

    I am from Nebraska, and I see Sirius on Orion's Belt.
     
  7. Dec 12, 2015 #6

    fresh_42

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    "Sirius can be seen from almost everywhere on the Earth's surface, with only observers north of 73 degrees latitude unable to see it, and it does not rise very high when viewed from some northern cities, reaching only 13° above the horizon from Saint Petersburg." (Wiki)
    Valentine is 42°N , rest is south of Valentine.
     
  8. Dec 12, 2015 #7

    The point being?
     
  9. Dec 12, 2015 #8

    fresh_42

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    You can see Sirius, as well as me, for both of us live south of 73°N, you live south of or near Valentine (42°N) as you've said, me on 50°N. However, although we can see Sirius, it's far from being near the sky's north pole. It's more south in the sky for even people in Australia can see Sirius.
     
  10. Dec 12, 2015 #9

    tony873004

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    I take this back. Sirius has a high proper motion, and it is traveling almost due south in our skies. It WILL become the southern pole star in 67000 AD, and again in 152000 AD.

    Polaris has a slow proper motion. It has been, and will continue to be the north star for a few more cycles before it moves too far from the polar locus .

    To illustrate, here are 2 simulations. On the left of each screen is a Play button [>] to begin the simulation. Next to the play button is [->]. This lets you run time into the past.

    This simulation shows how the northern pole stars change over time in 26,000 year cycles. Notice that Polaris doesn't move much in 26,000 years and once again becomes the pole star in the future. If you run it backwards in time, Polaris was the pole star 26,000 years ago as well. Notice how Vega becomes the pole star in 13000 AD, and Thuban becomes the pole star in 23000 AD
    http://orbitsimulator.com/gravitySi...1,4,465,1,4,530,0,4,660,1,260,30,1,260,200,40

    This simulation shows the southern sky. Notice that Sirius travels very fast across the sky as it is very close to Earth. It becomes the southern polar star in 67000 and 152000.
    http://orbitsimulator.com/gravitySi...1,4,465,1,4,530,1,4,660,1,260,30,1,260,200,39
     
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