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In article <3ou6e4$aia@mark.ucdavis.edu> szdefons@bullwinkle.ucdavis.edu (Eric DeFonso) writes:

>   R. Mounce <mounce@u.washington.edu> wrote:
>  >Sometimes, I'll admit, I think of the earth as flat.  There are even times
>  >(heaven forbid!) when my thinking is entirely consumed with the shapes of
>  >peaks and valleys.  But what I am interested here is a related concept -
>  >centeredness.  I have heard that some astronomers find it useful to
>  >discard the sun-centered model in much the same way as the earth-centered
>  >model became outdated.  Does anyone know if this idea of centeredness is
>  >changing its center? 
>  >

>  I'm not sure what you mean by asking this question, butI just wanted to 
>  comment on your statement about astronomerss discarding the sun-centered 
>  model. 
>   On the subject of celestial mapping, it is much simpler to 
>  continue to think of a geocentric universe. After all, the earth happens 
>  to be where all the observers are (Voyagers notwithstanding), so why not 
>  continue to treat the earth as the center when it comes just to the basic 
>  task of finding out where other objects of interest may be?
	
 This is true; right ascension and declination, the basic parameters we use 
 to locate an object's position on the sky (equivalent to latitude and 
 longitude) are Earth-centered.  But of course, this is just a convenient 
 approximation, because we're on Earth.  We do move cyclically about the Sun, 
 as proved by James Bradley's observations of the aberration of starlight 
 almost 300 years ago. 

 If you're doing accurate astronomical observations and want to know something 
 like the redshift of light from a galaxy, the exact period of a pulsar, or 
 something else, you have to do all kinds of corrections to take the motion 
 of Earth out of the equation.  You have to correct for rotation -- whether 
 the part of Earth with the telescope is going towards or away from the 
 celestial object; the motion of Earth around the Sun (including ellipticity), 
 the motion of the Sun in the galaxy, etc. 

>   In a more physical context, no astronomer I know treats even the 
>  sun as the center of the universe - in fact, modern cosmology 
>  acknowledges no place in the visible universe as the center. So the 
>  issue of whether astronmers are reconsidering replacing the center of the 
>  universe with the earth may simply be a misunderstanding of the 
>  application  geocentrism to the mudane topic of mapping.

>   just my 2 yen.

								Doug 




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	  Eric DeFonso        ##################################################
      Atmospheric Science     # If you lived in this .sig you'd be home by now.#
   Univ. of California, Davis ##################################################
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