Old device to measure star positions on photo plates?

What's the device called? There may be another device called a
comparator. If so, what does it do? Blink?

"W. eWatson" wrote

What's the device called? There may be another device called a comparator.
If so, what does it do? Blink?

The latter is callled a blink comparator, the device Clyde Tombaugh used to
discover Pluto.

On Sat, 05 Nov 2011 15:04:35 -0700, "W. eWatson"
wrote:

What's the device called? There may be another device called a
comparator. If so, what does it do? Blink?

The device used for measuring star positions on plates is called a
measuring engine (sometimes two-dimensional measuring engine, to
distinguish it from a one-dimensional measuring engine used just for
spectra). Of course, they're all collecting dust in observatory
basements these days, or sitting in museums.

A blink comparator provides a superimposed display of two plates,
which are alternately shown. This allows moving or changing objects to
be detected visually. These are museum pieces as well, although the
technique is still used for digital imagery. Virtually all
astronomical imaging software has a blink comparison function
included.

On Sat, 05 Nov 2011 17:32:05 -0600, Chris L Peterson
wrote:
On Sat, 05 Nov 2011 15:04:35 -0700, "W. eWatson"
wrote:

What's the device called? There may be another device called a
comparator. If so, what does it do? Blink?

The device used for measuring star positions on plates is called a
measuring engine (sometimes two-dimensional measuring engine, to
distinguish it from a one-dimensional measuring engine used just for
spectra). Of course, they're all collecting dust in observatory
basements these days, or sitting in museums.

There is a corresponding modern device though: the scanner. It
converts an image on paper or film to a digital image, and in that
process it must somehow position its pixels over the physical image.


A blink comparator provides a superimposed display of two plates,
which are alternately shown. This allows moving or changing objects
to
be detected visually. These are museum pieces as well, although the
technique is still used for digital imagery. Virtually all
astronomical imaging software has a blink comparison function
included.