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.

The Demon's Eyes

"What you look hard at seems to look hard at you."

(Gerard Manley Hopkins)

The other night at Carrs Mill, Richard Orr asked me whether I had ever looked at the "Demon Eyes". I had to admit that I had never heard of them. The Demon Star (Algol), yes. But Demon Eyes? Nope. 

Well, we had just been talking about the Water Jar over in Aquarius, which is to me to only recognizable asterism in that entire constellation. The rest of it is just a giant 4th magnitude mess - the worst place in the sky to locate anything by star hopping.

The Water Jar consists of 4 relatively bright stars, 3 of which (Eta, Pi, and Gamma Aquarii) form a tight little triangle with a fourth (Zeta Aquarii) right in the center. All 4 stars are approximately 4th magnitude, making the asterism naked eye visible, but not particularly prominent. (Some people, myself included, consider Alpha Aquarii, a 3rd magnitude star somewhat to the east of the other four, to be part of the asterism. But that's not important here.)

To the naked eye or through binoculars, Zeta Aquarii appears to be a run of the mill solitary star of a nondescript white color. Even when I turned my 90mm refractor over to it the other night (using a 13mm Nagler eyepiece), there was nothing worth mentioning about it. But when I swapped eyepieces for a 3.5mm Nagler... Wow! There was a stunning, easily splittable double star, the two components of apparently equal brightness. They looked eerily like a pair of (rather sinister) eyes staring back at me. Just who was observing whom?

The A and B components are a true double star, with an orbital period of approximately 540 years, and the system itself is about 92 light years away. Impossible to see telescopically, the A component is itself a double star, composed of an F-type main sequence star with a companion about one 3th its mass. They orbit each other every 26 years, so they must be extremely close to each other. As for the system's main components (A and B), their separation is thought to be about 140 AU.

It's that last figure which intrigues me the most, since Neptune's orbital diameter is 60 AU. So if you can imagine one half of the distance between A and B Zeta Aquarii, that's pretty much what our own solar system would look like at a distance of 92 light years.

As an experiment, I observed the pair with my 5mm Nagler eyepiece. I could still split the double, but it wasn't as "clean" as with the 3.5mm. So if you're thinking of taking a look yourself (highly recommended),  use all the power you have. It's worth it!