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Old 03-02-2010
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Effects on celestial navigation?

Howdy,

I was reading about the effects of the earthquake in Chile earlier on NASA's website ...
Quote:
Perhaps more impressive is how much the quake shifted Earth's axis. Gross calculates the quake should have moved Earth's figure axis (the axis about which Earth's mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth's figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet).

By comparison, Gross said the same model estimated the 2004 magnitude 9.1 Sumatran earthquake should have shortened the length of day by 6.8 microseconds and shifted Earth's axis by 2.32 milliarcseconds (about 7 centimeters, or 2.76 inches).
... and I was wondering, Do these shifts in the Earth's axis effect celestial navigation at all? Are they too small to to notice, or do those who use celstial navigation have to alter their calculations in some way to compensate for them? How much of a shift would need to occur before it starts effecting one's navigating? I have no experience at all in celestial navigation, but was curious to here what those with experience would say.

Thanks in advance for any info
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Old 03-02-2010
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Quote:
Originally Posted by PTKAR42 View Post
Howdy,

I was reading about the effects of the earthquake in Chile earlier on NASA's website ...

... and I was wondering, Do these shifts in the Earth's axis effect celestial navigation at all? Are they too small to to notice .....
Yes, they are way too small to make any difference to the celestial navigator.

Bill
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Old 03-02-2010
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Especially small craft celestial navigators...
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Originally Posted by btrayfors View Post
Yes, they are way too small to make any difference to the celestial navigator.

Bill
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Ah, I see. Thanks

How big of a shift would have to occur before it starting interfering with CN? Just curious.
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Wink

It affects you if you can normally fix your position with better then 3 inch accuracy.
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Quote:
Originally Posted by tomaz_423 View Post
It affects you if you can normally fix your position with better then 3 inch accuracy.
Hey, I can do it down to the millimeter, my friend (ha ha, just joking obviously since I've previously stated I have no experience with cn)

So I guess it would have to be a pretty big shift to effect thing then. Not knowing, I had wondered if the distance to the stars being navigated with might be a factor in that.

Thanks for the replies
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I hate when my sightings are thrown off by 2.7 milli-arcseconds. And even worse, it has shortened the day by about one millionth of a second as well, so my chronographs and tables are all going to be off as well.

Probably will cause a gross position error of at least one hundredth of a millimeter...anyone got a more precise figure for that?
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Buy Lein's Addendum to the Nautical Almanac for tables to compute Necessary and Essential correction Factors for your Altitudes and Azimuths arising from Earthquakes and other Tremors in S. America. New editions published with each major Quake. Derived via the latest theories and Methods! $29.99 + S/H, not sold in stores.
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"New editions published with each major Quake."
Can I get a yearly subscription with free updates? Or a discount for pre-ordering the next five quakes up front?
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