It's not easy being green

Yesterday out at Carrs Mill, I decided to make it a Green Star night. Yes, I am well aware that there are no such things as green stars - let's get that one out of the way right up front. But there are many stars that appear to be green when viewed through the eyepiece. The most famous is Almach, a.k.a. Gamma Andromedae, a spectacularly beautiful multiple star system not far from M31. At 2nd magnitude, it is an easy naked eye object, but it takes a telescope to see that it is not a solitary star. My 102mm refractor splits it into its A and B components, A being brilliant yellow, and B looking like nothing so much as a tiny Granny Smith apple nestled up against its brighter companion. Turns out that B is not a single star at all, but three, none of them being even remotely green. (see illustration below)

No possible amateur telescope can split B into its components. The easiest and surest way to determine its true makeup is with spectroscopy. Perhaps it's all those colors being mixed up that give us the impression of a single green star?

Now that we got the low hanging (green apple) fruit out of the way, we can turn to other greens that were not so easy to observe.

Struve 2725 in Delphinus is an absolute joy to behold. First of all, it, along with neighboring Gamma Dalphini, make up a delightful cousin to Lyra's Double Double. If you stop right there it's already a "must see" item on any stargazer's list. But amp up the power and zero in on Struve 2725, and drink in the subtle colors involved - a primrose primary with a dimmer, yes, green companion star.

Moving over to Cassiopeia, we check out Sigma Cassiopeiae, a star I never would have suspected of being double had I not been informed of this fact. I found it to be a difficult split, but my effort was rewarded by seeing a 5th magnitude primary of pure white, accompanied by a 7th magnitude bluish green secondary.

I had intended to wrap up the night by observing a 4th green star, over in Pegasus - Struve 2841. But alas, a cloud had moved over to obscure that part of the sky, and it showed no signs of going anywhere. So I saved that one for another time!

I was using my 102mm Stellarvue refractor with 9, 5, and 3.5mm Nagler eyepieces.