Is Zubeneschamali Green?

Sorry about this. I had better put this right, and I'll try not disturb anybody.

Beta Bootis is a star called Nekkar. It is a G glass star and is therefore plain yellow. There is no discrepancy about it at all.

It is Epsilon Bootes that we can have fun with its colours. And it is actually the 2nd brightest star in Bootes after Arcturus. Named Izar, its components are yellow orange and blue. Sometimes the blue star appears green -but not to me.

However, last night Tuesday 17th, Zubeneschamali had the slightest blue tint. No green tint for Valerie or myself.

I must keep an eye on it over the summer.

Aubrey.

Hi Aubrey,

Checking through my observations, there are a few doubles in which one component appeared to me to have a greenish tint - presumably an optical effect, as Dave said. Several are visible in the Summer skies, here are my notes:


66 Cet, STF231: Nice wide double, with yellow primary and distinctly fainter golden secondary that appears to have a hint of green? Better at 140X than 187X, because tighter.
STF2841 in Pegasus: Wide double, yellow primary, fainter secondary has a hint of green. Wide even at 88X.
STF1283 in Cancer: Pale yellow primary with a slightly fainter greenish secondary, well separated at 115x.
STF2110 in Hercules: Bright, pale yellow primary, widely separated from a very faint companion, that occasionally seems to take ona greenish tint.
Rasalgethi in Hercules: Brilliant orange primary, close to a fainter, distinctly greenish, secondary at 140x. Beautiful colour contrast, and a rich backdrop of stars - outstanding.
δ Her: Brilliant, pure white star, well separated from a much fainter companion at 140x. The secondary has a yellowish-greenish tint. Many other stars in the field , including a deep red one to the North.
ι Tri: Lovely pair. Bright, yellow primary and a somewhat fainter, but still bright, secondary that appears to have a distinct greenish tinge. Close, but nicely resolved at 100X.
τ1 Aqr, Aqr: Bright white primary, with a much fainter secondary that offers tantalising hints of colour, sometimes greenish, sometimes pinkish. 50x also shows the glorious orange tau Aqr.


Of course some of the planetary nebulae really are green or greenish blue, and the colour is clear in my C11. Here are some favourites:

NGC6210, Turtle Nebula in Hercules: Small fuzzy disk, with a beautiful green colour. Forms a triangle with a bright yellow star and a fainter copper orange one.
NGC6572 in Ophiuchus: Small planetary, forming a tight right angle triangle with field stars. distinctly greenish colour especially at high magnification.
NGC6891 in Delphinus: Tiny glow, with a hint of green by averted vision.
NGC7009 , C55, Saturn Nebula in Aquarius: Large bright planetary, with a greenish glow.
NGC7027 in Cygnus: Bright, distinctly greenish glow, in a sparse field.

Cheers,
Mike

I must re-check Rasalgethi soon. That is a brilliant double visible very easily in the Summer sky. Otherwise called Alpha Herculis for those who don't like names and difficult pronunciations. I split easily at 112X.

Aubrey.

Hi Gents, I have just spent the last few minutes looking at this star with the following:

William Optics FLT110 refractor
12mm type 4 Nagler eyepiece x64

A nice trick I have discovered was to defocus the star, it is definitely blue-white to me under a really transparent sky, the star itself is 21 degrees above the horizon with zero light pollution.

I can only conclude that it is indeed blue-white, even after bringing the star into very sharp focus, maybe a later night of not so good conditions may change my perception if colour??

I hope that this helps you Aubrey...

Keith..

Hi Keith. I know I am biased, but I do love these William Optics apochromatic refractors. They always kill false colours and therefore they give us very reliable sightings. Yep, blue white for me too for Zubeneschamali. Thank you.

Anyone else up for the challenge?

Aubrey.

Plain white through my NexStar SE8.

Patrick Moore also states that it is reputedly the only naked-eye star with a greenish hue, but that to his eyes it always appeared white. So we're in good company.