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For those of you who haven't figured it out yet, 1 parsec (pc) is the distance
at which the radius of the Earth's orbit subtends 1 arcsecond. So the
annual parallax, in arcseconds, is just the inverse of the distance in
parsecs. That's why the parsec is such a handy distance unit in astronomy. So,
for Polaris, with a distance of about 240 pc, its annual parallax is about
0.004 arcseconds or 4 milliarcseconds.

Although a bit dated, list members might be interested in the availability of
the UNB GGE Lecture Note No. 49 on geodetic astronomy, which can be downloaded
from the department web site. Caution: as a scanned document, it's quite large
(17 MB): .

-- Richard Langley, FRIN
   Professor of Geodesy and Precision Navigation

On Mon, 26 Nov 2007, George Huxtable wrote:

>
>Mike (isonomia) writes
>
>
>"According to WIkipedia polaris is at "2400 Astronomical units"."
>
>The moral of that story is-don't believe what you read in Wikipedia.
>
>"However, wikipedia gives the Parallax (?) is given as  7.56 � 0.48
>mas (minutes of arc),"
>
>No. mas means milli-arc-seconds. The distance of Polaris, 430 light years,
>corresponds to that arc.
>
>"so clearly I can't be like some and assert I
>fully understand the subject."
>
>Only too true, I fear.
>
>George.
>
>contact George Huxtable at george@huxtable.u-net.com
>or at +44 1865 820222 (from UK, 01865 820222)
>or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
>
>
>>
>
>


===============================================================================
 Richard B. Langley                            E-mail: lang@unb.ca
 Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
 Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
 University of New Brunswick                   Fax:      +1 506 453-4943
 Fredericton, N.B., Canada  E3B 5A3
     Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
===============================================================================

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