Stars in Stereo

[kirk bender <kbender@xxxxxxxx>]

>There was some discussion recently about whether or not the stars
>can be seen in stereo.
...
>Now the best stereoacuity I know of is 3" of arc. 
...
>and we did indeed possess a
>stereoacuity of 3" of arc, we'd have it made; we could see Rigil
>Kent standing out from the other stars. 
...
>John (Orthoman) B


Err... I don't know what you mean exactly by stereoacuity,
but a book I have says the eye's optics are limited to 1 arc minute of
resolution ( the diameter of a dime at 60m), and the human
retina actually sets it to about 3 arc minutes. Maybe you meant
arc minutes, rather than arc seconds.
The Astronomy book I have (Astronomy by Jay Pasachoff, 1993)
says that using the earth-sun distance
as a baseline (1AU, half the maximum possible), Proxima centauri
has a parallax (angle across the sky) of .772  seconds of arc.  It
says this is the angle subtended by dime at 5km. It says trigonometric
parallaxes can be measured for stars out to about 300 light years, and
this method can be used for only about 10 thousand of the stars
closest to us.  A parsec is the distance at which 1 AU subtends
only 1 arc second. (parsecs= 1/ arc seconds) 1 parsec = 3.26 light
years.  So proxima centauri is 1/.772 parsecs, or 4.23 light years.

Anyway, you need optics that can (at least) pick out a dime at 5km
to make stereo star pictures.  Before computer scanning,
astronomers would use a stereo viewer on pairs of plates from high
powered telescopes exposed several months apart to see if anything
moved, thereby discovering a close star (or asteroid).

If you want to see stereo images of stars, there is a book titled:
"3D Star Maps" by Richard Monkhouse and John Cox,
Harper & Row, 1989,  ISBN 0-06-016131-0, 96 pages.
It has computer-generated analglyphic red-green maps of the
sky, showing the stars' relative distances when you put on
the included glasses.  It's um... intriguing.   The fields are
just dots, so it is a little hard to visualize sometimes.
The maps are very detailed, showing the Messier and many NGC
objects. There are bright star maps (down to 6th magnitude-
dimmest naked eye), near star maps, galaxy maps and color (monoscopic) 
photos of objects. Worthwhile if you're into stargazing.

-----------------------------------------
kbender@xxxxxxxx (Kirk Bender) PSX addict
http://www.angelfire.com/free/kb171.html 



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End of PHOTO-3D Digest 1195
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