Posted by David G on August 15, 2015 at 17:53:26 from (75.167.202.204):
In Reply to: Continental Drift posted by David G on August 15, 2015 at 17:44:01:
Not to bring up a global warming debate, I always wondered if people took wobble in the earth into the equation.
I found this:
The motion of the Earth's axis has two parts -- precession and nutation. Precession is the motion of the axis in a large circle over a roughly 26,000 year period. Nutation is a harmonic with a roughly 18.6-year period, superimposed on top of the precession circle.
Although the axis moves, the equator always remains fixed with respect to the axis. The equator does move with respect to the ecliptic, but since GPS coordinates are referenced to an Earth-centered, Earth-fixed plane, this movement of the equator with respect to the Earth-Sun line is transparent to GPS.
NGA issues a new map datum every 5-7 years. This is simply a function of measurements being refined enough to warrant the issue of a new datum. It's not tied to any natural event.
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Today's Featured Article - Talk of the Town: The Saga of Grandpa's Tractor - by The following saga is from the Tractor Talk Discussion Forum. Someone. The saga starts with the following message: Hey guys I have a decision to make. I know what you all will probably suggest and it will probably agree with me way down inside, but here it is. I have a picture blown up and framed in my "tractor room" of a Farmall M. It was my Grandpa's tractor, of which whom I never got to meet. He froze to death getting this tractor out of the barn to pull a truck out of the ditch before I was born. Anyway my dad and aunt had to sell it at the auction,
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