Small Wonders: Cassiopeia A monthly sky guide for the beginning to intermediate amateur astronomer Tom Trusock 06-Nov-2005 Figure 1. W idefield map 2/15 Small Wonders: Cassiopeia Target List Object Type Size Mag RA Dec h m s α (alpha) Cassiopeiae (Schedar) Star 2.2 00 40 51.2 +56° 34' 23" h m s η (eta) Cassiopeiae (Achird) Star 3.5 00 49 26.6 +57° 51' 07" M 52 Open Cluster 16.0' 6.9 23h 25m 06.5s +61° 38' 33" NGC 7788 Open Cluster 4.0' 9.4 23h 57m 00.3s +61° 26' 11" NGC 7789 Open Cluster 25.0' 6.7 23h 57m 42.3s +56° 44' 41" NGC 7790 Open Cluster 5.0' 8.5 23h 58m 42.6s +61° 14' 41" NGC 147 Galaxy 13.2'x7.8' 9.4 00h 33m 31.5s +48° 32' 34" NGC 185 Galaxy 8.0'x7.0' 9.3 00h 39m 17.7s +48° 22' 22" NGC 281 Bright Nebula 35.0'x30.0' 00h 53m 20.8s +56° 39' 26" NGC 457 Open Cluster 20.0' 6.4 01h 19m 55.9s +58° 19' 29" M 103 Open Cluster 6.0' 7.4 01h 33m 46.3s +60° 41' 28" NGC 654 Open Cluster 6.0' 6.5 01h 44m 25.0s +61° 54' 54" NGC 659 Open Cluster 6.0' 7.9 01h 44m 48.2s +60° 42' 05" NGC 663 Open Cluster 15.0' 7.1 01h 46m 41.6s +61° 14' 56" Challenge Objects Object Type Size Mag RA Dec IC 10 Galaxy 6.4'x5.3' 11.2 00h 20m 44.3s +59° 19' 43" Maffei 1 Galaxy 5.0'x3.0' 11.4 02h 36m 45.8s +59° 40' 40" Cassiopeia t‘s time to pay homage to the Queen. In late fall and early winter we see the annual ascent of Cassiopeia, Queen of Ethiopia, wife of Cepheus and mother of Andromeda. (This is the rise of I the big W in the northern sky to those of you less versed in ancient lore, but more familiar with the night sky.) Although Cassiopeia is a late riser when compared to other members of her fam- ily, there‘s little question at least to this observer that she‘s the one in charge. Doubt me? Well, let‘s take a minute and examine the evidence, shall we? Obviously, compared to the rest of her family, she‘s a late riser. That‘s a given. While poor old Cepheus is up and about the busi- ness of running the kingdom, she hasn‘t even peeked above the horizon no, she gets to sleep in. And then there‘s the whole chair bit. She‘s the only one in her entire family that‘s seated! Now, my wife tells me it‘s because she‘s been up all night with the children, but in my book, poor old Cepheus has been up just as long and he‘s forced to stand! Finally as if you need more evi- dence – just take a look at her jewelry. Cassiopeia, being smack dab in the middle of the winter Milky Way is a true treasure trove for all sorts of flashy ornaments and it‘s those that we‘re in- terested in tonight. She does get her comeuppance of a sort while sitting in the chair, half the time she finds she's upside down. According to some sources this is punishment for her boast that she was even more pleasing to the eye than the sea nymphs. Ahhh, vanity. Well, on to the celestial targets. First off, we‘ll take a look at a few of her solitaires: Alpha – bet- ter known as Schedar, Eta – or Achird, Gamma, Iota and – well, what was once one of her shin- ing jewels – Cassiopeia A. Schedar is the brightest star in Cassiopeia, although not by much and not all the time as it can be surpassed in brightness by the variable star Gamma. Gamma itself is unique as it‘s held by some to be a binary star system that contains a Be star and a neutron star and is the brightest x-ray binary star in the night sky – to my knowledge no other x-ray binary can be seen with the naked eye. Trivia – the first voyagers to the Centauri star system will see Sol near epsilon at about .5 mag in brightness. Tom Trusock 06-Nov-2005 Small Wonders: Cassiopeia 3/15 Achird is a well known binary that the NSOG informs us was discovered by Sir William Herschel in August 1779, the period is around 500 years, and the separation varies between 5“ and 16“. It‘s purported to see be multiple colors – heavily dependent on the aperture you use to view it with. Take a look for yourself. Cassiopeia A (RA 23:23.4, Dec +58:50) is the youngest known supernova remnant in our galaxy having exploded sometime around 1667. Opinion on who was the —discovery“ observer is di- vided – some feel that John Flamsteed cataloged it on August 16, 1680 – others point out that the —star“ he cataloged has nothing exactly corresponding to its position, and that he simply made an error. Other than that, the first time it stepped into the limelight was in the late 1947‘s when it was cataloged as the strongest radio source in the sky (excluding solar system objects) and given the designation Cassiopeia A and received the designation 3C 461 in the third Cambridge survey. While it‘s not a visual target per-se, it is a fairly interesting object located in Cassiopeia. Iota Simon Walton – one of our longtime readers. You can get an idea of the main difficulty you'll be facing. Iota's actually a triple star. To give you an idea here, the magni- tudes are 4.5, 8 and the closer companion is listed as mag 7 (you'll probably need at least a 4" to see all three). While her stars are interesting, there‘s no denying that they are far from the only attraction. Cassiopeia is rich in targets, particularly open clusters. What else would you expect? These are the spectacular, shiny objects that fa- Figure 2: Iota – Simon W alton vored of a queen. Other targets? A search of the database reveals that (brighter than mag 13.5) there are: 7 galactic Iota is a challenging triple, namely targets, 1 quasar, three planetary nebula (the brightest in seeing how small of an aperture IC 289 at mag 12.3), 4 —bright“ diffuse nebulae, 138 dark and low of a magnification can nebulae, and 43 open clusters. Clearly there‘s plenty here split it – take a minute if you to keep an observer busy for a LONG LONG time. have clear skies and give it a go. Here‘s an image contributed by NGC 7788, NGC 7789 and NGC 7790 For the DSO‘s this month, we‘ll start with the western edge of the W, and follow along hitting our targets as we go. Just a few short degrees from Beta, we find three objects worthy of telescopic inspection. 06-Nov-2005 Tom Trusock 4/15 Small Wonders: Cassiopeia Figure 3: Area map of Beta and NGC 7789, 7790 & 7791 First up, we‘ll stop at NGC 7789. This has to be one of my all time favorite open clus- ters. Ok, sure, you probably hear me say that nearly every month, but hey – it‘s true! And doubly so this time. This object looks amazing in nearly any size tele- scope. I‘ve viewed it with scopes as small as 60mm refractors to monster 20 inch dobsonians – and they all had something to offer. Smaller scopes can expect a mist that breaks into pinpoints of light as con- ditions or aperture increases. Large scopes can see hundreds of individual stars that, to me, have a very evident rose or whirlpool effect – although to the best of my knowledge, I‘ve never heard any other observer describe it that way. If you have a large scope, please take a look and tell me what you see. Is this simply my over- active imagination at work? Or is my brain pulling out a subtle pattern but existing pattern? Intermediate scope users most likely won‘t see any sign of the whirlpool, but they will see an extremely rich concen- tration of both resolved stars and the background mist that indicates hundreds more lying just beyond the resolution lim- Figure 4: Sketch of NGC 7789 – Eric Graff its of their equipment. Tom Trusock 06-Nov-2005 Small Wonders: Cassiopeia 5/15 This cluster should be visible with any form of optical aid, and I‘d suspect you could even see it naked eye from a suitably dark and transparent site. Anyone care to put this theory to the test? Eric Graff‘s wonderful sketch is an excellent depiction of what to expect through a 4œ6 inch tele- scope from a moderately dark site. Next, lets head just north, and over to a As you can see, there are a total of six clus- chain of clusters – the two brightest being ters in the immediate area, five of them in a NGC 7790 and NGC 7788. chain. For the small scope user, simply con- centrate on finding 7790 and 7788. These two clusters are the brightest in the chain and will probably be seen as a general mist with a few defined stars from a moderately dark site in a small telescope. The other clusters I‘ve found to be more of a target for larger telescopes, detailed maps and much patience.