Re: Furthest stereo?

[P3D KENNETH LUKER <KLUKER@xxxxxxxxxxxxxxxxxxxxxxx>]

>From Paul Kline: 
> While watching comet Hale-Bopp this weekend I got to thinking, what is the
> furthest stereo distance yet captured?  And also, how long before the
> Andromeda Galaxy has rotated sufficiently that one could take a current
> pic together with an archived pic and have a stereo combination?
> 
> We should get out and watch the stars more :-)

 
I think that in a millenium or ten we may see some movement in 
the Andromeda Galaxy, but I'm not holding my breath.  

We're all familiar, I expect, that the standard for distance
measurement celestially is based on the same concept as stereo
vision, parallax.  The light year is the distance traveled by light
in a year, but a parsec is the distance of an object that has a
parallax of one second of arc when using a viewing baseline of one
astronomical unit, the sun-to-earth distance. (Or is it twice that? 
I can't remember!)  There isn't much stereo information in a
displacement of one second of arc (one 3,600th of a degree), so
there isn't much use in taking pictures of the sky six months apart
and making a stereo pair.  It would be more effective just to take
pictures several years apart of those stars known to be in rapid
true motion against the background, and then make pairs of those
pictures.  The result would not truly be representative of real 
distance difference, but it would appear to be stereo, just as 
pictures of Hale-Bopp taken sequentially with an intervening time 
lapse can make a stereo pair that makes the comet appear to be nearer 
or farther than the field stars.  

I've had some fun with my astronomy program that allows me to display 
a region of the near milky way galaxy, then rotate it slightly.  When 
I look at the two views, I can see the nearby stars or chosen 
constellations in stereo.  Nice for a gimmick, but certainly not 
observable in truth until Jean Luc Picard's time, when it comes.

Yes, go look at Hale Bopp just after sunset this week!

Ken Luker
 


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