A quick question about "precession" of the earth

Discussion in 'Astronomy, Exobiology, & Cosmology' started by kingwinner, Oct 15, 2005.

  1. kingwinner Registered Senior Member

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    Precession says that the direction of the Geographic North Pole that is pointing is changing with a long period of time.

    So when the precession occurs, in a period of a few thousand years, would that possibly make summer to occur from February to June, Spring to occur from October to January? Because if the direction of the Geographic North Pole that is pointing is changes, using the fact that summer solstice occurs when the north pole points toward the Sun, this day would occur in some other time in the year, no longer on June 21-22. And also, precession does not change the tilting of the axis of rotation! (precssion occurs but keeps the tilting the same--at 23.5) Am I right?
     
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  3. Lucas Registered Senior Member

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    No, our actual calendar is based on the tropical year, and this kind of year makes corrections to the precession of Earth's axis, so the summer solstice will always occur on June 21-22

    Yes, the tilt of the axis stays always around 23'5 degrees, but varies slightly (it gets from around 22 degrees to around 24 degrees) during a cycle of a lot of years
     
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  5. kingwinner Registered Senior Member

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    Why? If the axis of rotaion (North Pole) is pointing a different direction, the North Pole should no longer be tilting toward the Sun on June 21-22, but at some other time...
     
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  7. Lucas Registered Senior Member

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    447

    Well, this was a problem in other times, because there was a time when the first day of spring had a difference of more than ten days with respect to its original date. However Pope Gregory decreed that the summer solstice must occur always at the same date, and adopted the tropical year as a basis of the calendar. So, our current calendar, the Gregorian calendar makes rectifications to counter the precession of the axis
     

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