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B Solar Eclipse by a Black Hole

  1. May 4, 2018 #21
    It was my understanding that the axis already teeters and that the moon helps keep it from going out of control. Also that the zenith will eventually change from polaris to another star (name is escaping me). So wouldn't the earths axis eventually go out of control without the moon to help regulate?
  2. May 4, 2018 #22


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    If "teeters" means precession, the moon causes that, it doesn't mitigate it. If it is something else, it would still need a cause.
  3. May 4, 2018 #23
    Here is kind of what I'm trying to explain. It's under the seasons part.

  4. May 4, 2018 #24
    I found a number of non crazy sites where this is discussed, and the answer seems to be to with tidal interaction/ torque.
    Here's an example (Paragraph 4)
  5. May 8, 2018 #25


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    The magnetic poles of the Earth have apparently flipped in the past, and will possibly flip again in the future. If everyone continued to believe their magnetic compasses for direction, Europe would then be in the Southern hemisphere, Australia would be in the Northern hemisphere and the sun would rise in the West and set in the East.
  6. May 10, 2018 #26


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    From the link:
    Um, what? Bait-and-switch much? If your head isn't spinning, it gets even worse:
    So this "might" happen in a few hundred thousand years -- or a billion -- or never. What this sounds like to me is that scientists have speculated this may be a "thing", but have never actually even modeled it. So it might be a thing or it might not, but certainly not for hundreds of thousands of years or few orders of magnitude longer.
  7. May 24, 2018 #27

    Ken G

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    The cause is the other bodies in the solar system, which have weak effects but start to matter when there are resonances. Both the Moon and the Sun provide the torques that produce the 26,000 year precession, and the precession interacts with the eccentricity of the Earth's orbit to produce climate effects. The potential for various Milankovitch-type cycles makes this a complicated question, but it is certainly quite possible that the presence of the Moon alters the nature of these cycles, and may affect habitability. An influential paper here is Laskar et al. 1993 (https://www.nature.com/articles/361615a0), which asserts that faster precession (assisted by the Moon) helps shorten the time that influences from other planets could destabilize the Earth's axial direction. However, the situation is quite complicated (see https://davidwaltham.com/wp-content/uploads/2013/03/EPSC2013-37.pdf), and the entire area of Milankovitch cycles produces a lot of debate about ice ages and other habitability issues. The fact is, at present we don't really understand exactly why the Earth is so habitable, or how other planets might not be, but there is plenty of potential for anthropic-type selection of the special conditions on Earth, particularly its massive moon.
  8. May 24, 2018 #28


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    not apparently has … they have flipped many dozens of times and there is no reason to suspect they wont in the future :smile:


    this is incorrect

    the magnetic poles flip, NOT the geographic poles so my home of Australia, will still be in the southern hemisphere and on top of that ... the Earth will still continue to rotate in the same direction

    The northern and southern hemispheres/poles are defined by our geography "labels", not the magnetic polarity.
    If it was by magnetic polarity,. The "North" magnetic pole is in the southern hemisphere just off Antarctica.
    The "South" magnetic pole is in the north of Canada region ( approx)

    The "North" pole of the compass needle points (is attracted to) the South magnetic pole.


    and from Wiki ....

    my bold

    Last edited: May 25, 2018
  9. May 24, 2018 #29
    I think we can agree that the unpredictability of Earth's magnetic poles is weird though,
    Is there any mainstream theory which it explains it?
  10. May 25, 2018 #30


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    not that I have so far read
  11. May 25, 2018 #31


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    Maybe not specifically, but the general idea is that the liquid core is not spinning consistently with the rotation of the Earth, but rather has some additional bulk movement. Exactly why and how is not really known, but given the planet is geologically active, I don't see this to be a shocking phenomena.
  12. May 25, 2018 #32
    From my astronomy 101 class I learned that much like the sun, the magnetic lines get tangled and break causing the pole swap and that we experience it at a far slower rate than the sun.
  13. May 25, 2018 #33


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    Get in a rocket ship and fly west at greater than the Earth's rotation rate. Eventually you'll catch up with the sun.

    Edit: alternately, wait till sunset and go up a tall elevator. The sun will rise again over the western horizon.
  14. May 25, 2018 #34


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    To return to this point: (1) This is 35 arcminutes, or about 4 (temporal) minutes of Earth rotation. (2) Doubling this effect would require increasing the atmospheric density by ~40% [I think, or maybe ~ 100%?] in those 4 minutes of time.

    If you see such an effect, it can't be caused by weather. Extreme storms cause atmospheric density to change by ~ 10% over a few hours. So it's presumably caused by a dinosaur-extinction meteoric event.

    The corresponding overpressure will travel at somewhat more than the speed of sound (~1000 km/hr), which is just about the Earth's linear rotation speed at mid-latitudes. So it will reach you in less than 4 minutes, and you will die before the second sunset finishes. I hope it's a beautiful one, at least.
  15. May 25, 2018 #35

    stefan r

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    Huge mirrors could do it. Maybe 2 mirrors with 1.7 km radius with one orbiting at 380km. You would need to go slightly larger to compensate for any angles. Something much less bright than the Sun could resemble the Sun setting. Also a bent mirror could focus light so something smaller than the Sun's angular diameter could appear just as bright. If you want the pink/purple across the horizon effect you could use an array of small mirrors. Not sure why we would do that. Could also put a mirror on a balloon, tall building, helicopter or mountain and reflect the sunset. There is no need for the mirrors to be in the west.

    The town of Rjuken in Norway and Viganella in Italy have a artificial suns in the winter. Should work at sunrise for some part of the year. They are set up to bring in a noon sun.

    You can buy lights that make artificial sunrises for an alarm. It is supposed to help you wake up. Here is a mechanical artificial sunrise. You could set that in the north and south side of your room too.

    Mar's moon Phobos rises in the west, so does the international space station.

    In operation Hardtack Teak the USA detonated a nuclear missile in the atmosphere. At some places on the horizon it would have somewhat resembled a sunrise.

    There is also atmospheric effects that cause light to distort or flicker. Stars twinkle. Here is a video of a green flash. I would not say that the sun "rises again" but the edge can go over the horizon and briefly reappear.
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