Friday night proved to be somewhat of a new "revelation" for me on the
observation of close visual binaries. The sky was generally quite hazy
and disappointing for just about any kind of serious observing, so at
first I was a bit reluctant to take my scope out.
But I knew that looking at colours of brighter stars and close
binaries would be just about o.k.

When I started to examine the white pair of stars making up Epsilon 2
Lyrae (one of the naked eye stars of the famous 'Double Double') at
300x on my Skywatcher 8-inch, I was quick to spot that they were split
apart with an unusually large amount of room in between... I found it
hard to believe such a view! These two stars are just 2.3" apart in
angular separation and previously always appeared as two blobs of
light in my eyepiece with a hair line thin bit of blackness separating
them.
On this night however, as the summer air was exceptionally hot and
still, the two stars looked *miles* apart! Each component of Epsilon 2
Lyrae had several diffraction rings around it with a circular dot in
the core (the Airy disk) and the cores of the two stars were separated
by a distance that could easily accommodate at least another two
"cores" of the same size. On this basis, I made an estimate that my
8-inch newtonian could have split the two stars had they been as close
as 1.0" or even as close as 0.8" in separation. That would be
*dangerously* close to and approaching my theoretical Dawes Limit of
0.57"... I then turned my scope to the star Mu Draconis, another
binary nearby in the sky and also of approx. 2.3" separation. Again,
the same *miles* apart resolution of the two near-equal brightness
stars.

I then recalled someone telling me back in the Spring that they can
split the star Gamma Virginis when it was just 0.8" apart (this binary
pair is now very close to periastron in its orbit) using an 8-inch. At
that point I thought "Hmmmm.... that's probably because you have a
super-collimated, catadioptric, super-Maksutov class of apochromatic
beast with superior optics costing thousands... way above my league."

How wrong I was. It seems the atmosphere is a BIG decider when it
comes to binary separations and not necessarily always the aperture or
the magnification or the cost or quality of the telescope.

What a "revelation"...

Question: Has anyone ever managed to match Dawes Limit with their
instrument?! Or is that a pie in the sky goal never ever to be
attained?

Abdul Ahad
http://uk.geocities.com/aa_spaceagent/astronomy.html