Astronomy Question: Change of Seasons?
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Sam writes:
We discussed the seasonal change of summer to winter when I was in school and the years required to make the seasonal change from summer to winter and back to summer was 27,000 years.
Is this the number of years for this change and is this the same time period for a polarity shift of the poles?
Thanks Sam.
Sam, the phenomenon you are referring to is known as precession, where the axis of rotation “wobbles” with a specific interval.
You are correct in that this cycle is in the neighborhood of 26,000 – 27,000 years.
Keep in mind, not only does the Earth’s rotational axis “wobble”, the amount of tilt also varies in a cyclic pattern from around 22 degrees to almost 25 degrees.
There are some theories that use the axial tilt and axial precession (along with a few other orbital factors) to explain such phenomenon as “Ice Ages” – however, there is no known correlation (that I’m aware of) between these cycles and magnetic pole reversals.
While Geology isn’t my specialty, if I remember correctly, the last magnetic pole reversal was almost 800,000 years ago, and the reversal before that was around a million years ago. Some magnetic reversals took place over many years, and there are some magnetic reversals theorized to have taken place during a decade or less!
What is interesting to know is currently, the North Magnetic Pole is drifting over thirty miles per year from it’s current location in northern Canada, towards Siberia. Another interesting tidbit, is that while the North Magnetic Pole is geographically “North”, electrically, it is a south magnetic pole, in that it attracts the north “pole” of a bar magnet!
Ray Sanders is a Sci-Fi geek, astronomer and blogger. Currently researching variable stars at Arizona State University, he writes for Universe Today, The Planetary Society blog, and his own blog, Dear Astronomer
2012-12-04 08:05:41
Source: http://www.dearastronomer.com/2011/01/31/change-of-seasons/
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