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What will be the change in celestial coordinates in 50 years? 
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#1
Feb913, 02:10 PM

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Is it possible to use celestial coordinates which were taken 50 years ago? What kind of inaccuracy can we expect (give the answer in degrees)?
Could I say that it will be about 0.3° error assuming that around the year 130 BC, Hipparchus compared ancient observations to his own and concluded that in the preceding 169 years those intersections had moved by 2 degrees? 


#2
Feb1213, 01:14 PM

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P: 2,280

More like about 0.7 degrees.
1) 2 degrees is a rounded number, so you may as well say you're talking about 1/3 the time Hipparchus was. (A more accurate number would be about 2.4 degrees, in which case it would become worth comparing the actual ratio between 50 years and 169 years.) 2) A more accurate (although still inaccurate) estimate would be a 26,000 year precession cycle, meaning a change of about 0.14 degrees per year. Multiply by 50 to get about 0.69 degrees. 


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