Open Clusters And Colorful Doubles

Tonight should be the start of Mars passing in front of the Beehive open cluster.

It’s Wednesday morning as I type this.

[Today’s post is one of those I’m typing up without notes, so I’m sorry if things seem a little rambling.]

Right now the sky is generally clear. We have some lake-effect clouds blowing in from the east, but often those clear up completely by evening. The forecast is for clear skies tonight.


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Last week Thursday or Friday I observed the Beehive for the first time in decades. It really made an impression on me. In fact, my whole observing session late last week made an impression on me. I’m still thinking about it.

I observed three things.


I started with the Beehive. The whole constellation of Cancer was invisible to my plain eyes in the light polluted skies here south of Chicago. With binoculars I was able to see Delta and Gamma Cancri easily enough. Through my binoculars the Beehive was a just barely visible smudge between the two stars. But through my telescope the Beehive was fantastic.

That whole experience made me very thoughtful for some reason.

I mean, the whole business of pointing up at a seemingly completely empty area of the sky where nothing is visible, then zeroing in on one particular spot within that empty area of sky, and seeing something beautiful.

I’m still thinking about that. Where there is nothing, there can be amazing, even profound beauty if you just know to look there and take the time to do the looking .  .  .

I’m not sure what to make of that or why it has stuck in my mind, but I’m still thinking about it.


After checking out the Beehive, I star-hopped a few degrees north to a double star I had read about but never observed, Iota Cancri.

Just like the Beehive, this was an exercise in looking closely.

Iota Cancri was invisible to my plain eye. It was barely visible as an anonymous dim star through my binoculars. Even at low power through my telescope Iota Cancri appears as a plain, dim star.

As I increased power, however, at about 72x, I began to see Iota as a double star.

At 100x I saw the most remarkable colors I’ve ever seen in a double.

One component was blue. I’ve seen blue stars before. Beta Capricorni has a blue component and so does Albireo. Wikipedia has a pretty good picture of Albireo that captures something of the blue color. This is pretty cool because when you see it in real life it actually looks that way. It’s not a white star with a hint of blue glare. It’s an actual blue star. Robin’s egg blue. What a watercolor painter would call cerulean blue. Very cool.

It’s the second component of Iota Cancri that actually made me say, ‘Wow,’ out loud when I saw it.

Beta Capricorni has a white partner. Albireo has a beautiful orange-yellow partner.

Iota Cancri has a golden partner. It really is a kind of rich, glowing gold color. It’s not topaz yellow. It’s somehow darker and richer. It really is gold.

The combination of blue and gold is something I’d never seen and never expected to see.

I’ll do a sketch of Iota Cancri one day, but I want to observe the star at higher power.

With my small scope, 100x is about as high as the objective lens will support. But I have a barlow lens that lets me double the power of all my eyepieces. The results usually aren’t great, but point sources of light like stars are sort of ‘best-case’ scenarios for using excessive power. Sometimes it works out okay.


After looking at Iota Cancri I shifted positions and checked out the northern sky.

I star-hopped from the Big Dipper to the Little Dipper and down to Polaris. I wanted to observe, again, the Engagement Ring asterism. [Polaris In The News And Out ]

Polaris is so dim it is always difficult for me to find if I don’t check it out regularly. I actually had to star-hop first to Kochab in the ‘bowl’ of the Little Dipper and then, binocular field by binocular field, star-hop down to Polaris at the end of the ‘handle.’

That worked. But the sky is so poor around here that I couldn’t see the Engagement Ring with my binoculars. With my telescope at its lowest power, however, I was just able to get Polaris and the Engagement Ring in one field. And it’s still very beautiful, too.


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So, that was my observing session late last week. An open cluster, a colorful double and an asterism.

These are very good targets for a small scope like mine.

The thing is, ‘extended’ objects like a nebula or galaxy or globular cluster do not have defined edges. They are not point sources. Their apparent magnitude is spread over a section of sky and the gradient edges make it hard for our visual system to separate them out from the light polluted sky in the background.

This becomes clear when observing the Beehive through binoculars. Even though the Beehive has an apparent magnitude of around 3 and Iota Cancri has an apparent magnitude of around 4—so you would think the Beehive would be brighter and easier to see in binoculars—the opposite is true. Iota Cancri, though dim, is easy to see and the Beehive appears as a ‘smudge.’ That is how our visual system responds to minimal changes in contrast where the difference is sudden change versus a gradual change.

We see the sudden change easily but the gradual change is hard to see.

That’s why open clusters and double stars are great targets for small scopes. They both resolve to point sources. They both resolve to individual stars. (Although open clusters to the eye can be extended objects, through a telescope they resolve to stars. Unlike, say, globular clusters which only resolve to star in large telescopes.)


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I had such a good time looking at the Beehive and the colorful double Iota Cancri that I’m thinking of dedicating all my observing time this summer to open clusters and colorful doubles.

There are lots of both.

I don’t know of any good books that list colorful doubles, but over the years I’ve saved clippings from astronomy magazines and I have quite a few articles dedicated to colorful doubles. There are websites dedicated to colorful doubles and I’ll look around, find some good ones and link to them.

Gary Seronik’s great book, “Binocular Highlights,” lists 35 open clusters. And that list isn’t exhaustive, it’s just the ‘easy’ ones.


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So, that’s what’s up astronomy-wise right now.

I’m still giving a lot of thought to that business of seeing beautiful stuff where there appears to be nothing at all.

I’ll probably be dedicating this summer to open clusters and colorful doubles. Oil pastel works great for impressionistic renderings of both. (Oh, and I’ve found a great site where a guy makes realistic renderings of colorful doubles. I’ll link to that in another post.)

And tonight Mars should start its passage in front of the Beehive.

The skies are jumping!