Regal Gems

One of the best aspects of amateur astronomy is the rhythm of the seasons as reflected in the night sky. As we move deeper into fall we have the return of the familiar "W" asterism in the northern sky - Queen Cassiopeia. The constellations that we bid goodbye to in spring now return. It’s like visiting a familiar vacation spot - we want to see those tourist attractions but we also relish a chance for new road trips and opportunities to experience new vistas.

Like any proper monarch our queen is adorned with jewelry – open cluster are littered across the confines of this constellation. We often think of the northern terminus of the Milky Way to coincide with Cygnus, but that perspective arises from residing in the east coast light corridor. Even when we slip away to darker skies it is rare to get a good appreciation of the winter Milky Way as it flows through Cassiopeia and Auriga. I recall many years ago my friends Bill and Doris Burbridge had a place in western Maryland that they observed from. They invited several of us up one October evening for some observing. Perhaps it was just a night of wonderful transparency coupled with minimal light pollution but the sky was stunning. You readily saw the winter Milky Way, and clusters that I had to tease out from Towson were screaming their presence. Evenings like those constitute an astro-high that we photon junkies of the universe constantly want to recreate!

Setting up in my driveway I am confronted by the realities of suburban living as I strain to see Kappa, the faintest of the six stars that outline the queen’s seat in the heavens. I align the mount and set my 80mm Vixen upon it. First stop this evening is a visit to my friend the Owl, a.k.a. NGC 457. This fun cluster is bright, an easy star hop, and has more than enough stars in it to be readily recognized as an open cluster. The two brightest stars form the eyes of the wise bird, and the fainter members to the northwest constitute body and outstretched wings.

NGC 457

The avian eyes, Phi¹ and Phi² are not only beautiful but amazing suns. Phi¹ is actually a yellow supergiant (bordering on hypergiant) that is some 65 times larger than our Sol and, according to Hipparcos data, an absolute magnitude of -7.8! Think about that for a moment – that value represents an object 40x brighter than how Venus appears to us. For comparison Sol has an absolute magnitude of 4.8, so in a sky where all stars are placed at the same distance from the observer, Phi¹ is an incredible beacon that’d be easy to see in our daytime sky, while our Sun would be lost in the light pollution from most of our region. That’s one heck of a star! The companion star (not a true double) is a blue supergiant checking in at some 83,000 times more luminous than our Sun. So together the Owl’s gaze represents stellar furnaces of a scale that we humans find hard to truly appreciate.
I admire the cluster at 30x, a beautiful object set amid a wonderful star field. I think I can see a slight yellow cast to Phi¹ but it may be my imagination. There are probably close to two dozen cluster members that make up our feathered friend in my eyepiece. I have my camera prepped and ready to go so I take the time to grab several 25 sec shots that can be my indoor entertainment on a cloudy night as I process them.

The next item I want to attempt is NGC 7790, an open cluster NW of Beta Cassiopeiae that I saw years ago working the Herschel 400 list using my 6” reflector. As I recall it was small but pleasantly rich. I’m just not sure I can snare it from this location with my 80mm refractor but it seems worth a try. As I am panning the area in my quest I see another old friend pass through the field. This queen of ours has placed two gems – a sapphire and a ruby – together in her collection of double stars. Known as WZ Cassiopeiae, the primary is a ruddy 7th magnitude carbon star while the companion lying about an arc-minute due east is an 8th magnitude spectral class B (as in blue) star. The relative closeness in magnitudes, the easy separation, but especially the red-blue contrast – all add up to make WZ a fabulous if unsung double star. I linger on it, trying different magnifications to see which eyepiece gives the most aesthetic result. Smaller aperture scopes usually do not have enough light gathering power to do color justice, so I’m really pleasantly surprised how well WZ holds up under a smaller instrument. I decide to swap in the camera again to grab a few shots of my colorful friend.

WZ Cas

Back to my search for NGC 7790. I pan the region, critically examining each field for hints of a cluster. Finally I notice something – a small patch that is exhibiting that ultimate tease of barely showing some stars with averted vision but never robustly enough to allow you to position them in a sketch. This has to be a cluster, likely my quarry. It does have one star that can be seen, perhaps 9-10th magnitude, on the cluster’s trailing edge. The body appears as an ellipse of unresolved nebulosity that is at least partially, if not entirely, based in faint stars just beyond the aperture’s reach. With clusters like these it is easy to understand how over a century ago astronomers were suffering from aperture fever in an effort to prove that all nebulae were collections of unresolved stars. How fortunate for us they were wrong and we instead have a far more interesting universe to explore. I sketch the view of this attractive cluster for later confirmation and then start to break down the equipment due to the hour and my body saying it’d had quite enough cold weather observing for one evening.

In hindsight I wish I had grabbed a shot or two of this one as well, because when I went to confirm it the (ahem!) stars didn’t align. Ok, so what was it then? Well I likely need to revisit and grab a better sketch or a couple images but I’m thinking I landed on next door open cluster NGC 7788. It has the same orientation and, most importantly, that single bright star on its trailing boundary. So that’s my working theory and good excuse to observe again the next opportunity I get.

This serendipitous uncovering of a new (for me) cluster served to highlight how there are often little treasures out there that we pass by either in our haste to get to the main target or simply because we didn’t know to look for something. A few days after my session Richard Orr posted his observation of NGC 436, an open cluster below the feet of the Owl. (Richard also gave a vigorous defense of NGC 457 being a Dragon Fly – but certainly an Owl is a far more regal creature for Queen Cassiopeia!). His posting made me realize I had overlooked it while soaking in NGC 457. It was clearly in view – the picture serves as incriminating evidence of my oversight. So now I have yet another item for my agenda the next clear night – observe NGC 436 with intent!