Delta Cygni

[chiltonstar]

There seem to be quite a lot of different descriptions of the colours of this close pair. The Cambridge DSA describes them as "blueish white and greenish or ashen", although there are other accounts on this forum describing very different colours (eg red for the minor star).

Although I've looked at this pair many times before, it's always been with a 4" achromat refractor, which obscured the true colour because of chromatic aberration. I tried last night with my 5" Mak for the first time - try as I might last night (excellent seeing!), I couldn't really see any marked colour difference between the pair; the main star was white, with perhaps a blueish hint (may be refraction though) and the minor star, like a brilliant dot on or close to the diffraction ring of the primary was also white to me. Is this an individual eye thing, or is aperture important? I was using a 5" Mak at x190 and x250.

Chris

[carlc]

My guess is that both the things you mention are important (aperture and eyes) - it seems atmosphere may also have an effect: http://www.carbonar.es/s33/Articles/ColorinDoubleStars.pdf

Others have noted differences in colours for doubles (but give no explanation).

Finally:

Keep in mind, the colors of a double star are very subjective. There are several reasons. When the secondary is much fainter than the primary, the condition of the sky, the color-sensitivity of the observer, and the aperture of the telescope. The colors of bright binaries are best seen thru binoculars. And our eyes are more yellow sensitive since we all look to a big yellow sun.

from http://users.compaqnet.be/doublestars/

Hope this helps.

[lunator]

Chris

Your experience sounds about right

I find that in my Mak or Newt the star colours are fairly muted but in my refractor they can show very different hues

The scope people use and everyone differnet colour perceptions do make star colours a very individual experience.

Cheers

Ian

[NGC 1502]

I tried Delta Cyg a few nights back, with a 6" F6 Dob I've been refurbishing. I couldn't see any colour, but was chuffed to get a nice split of this quite difficult double.

Also got a split with my 70mm Pronto, didn't think it could be done with such a modest aperture, definitely no star colours this time, the Pronto is very sharp, but a

bit of CA doesn't help.

Regards, Ed.