Xi ( ξ) Cephei (Kurhah)
RA: 22h 04m Dec: +64° 38′
Mag: 4.4, 6.4 Sep: 7.9″ PA: 275°
Dist: 100 ly
Spectral Classification: A3
ΟΣ461 in Cepheus
RA: 22h 04m Dec: +59° 49′
- AB Mag: 6.7, 11.4 Sep: 11.1″ PA: 297°
- AC Mag: 6.7, 10.0 Sep: 88.9″ PA: 41°
- AD Mag: 6.7, 7.8 Sep: 184.7″ PA: 73°
- AE Mag: 6.7, 11.4 Sep: 237″ PA: 38°
Note: Click image at right to see all the data on this complex system from the Washington Double Star Catalog.
Five star isn’t a quality rating -it’s how many visible stars there are in this combo – or perhaps more if you apply enough light grasp. But let’s start with Xi ( ξ). It’s a piece of cake to find and yummy, too!
Haas rates it a “showcase” double and it deserves the title. Xi ( ξ) is an easy split – a 4.4 lemon yellow star and a 6.4 violet companion almost 8 seconds apart. While a 60mm should handle it, I found it very easy with the 76mm, even at 38X – and just plain pretty when I used a 13mm Plossl delivering 92X. I found it with no trouble on the night of a full moon – in darker skies it would be even easier. Cepheus forms a crude “home plate” with five bright stars, the faintest approaching magnitude 4. In the middle of the square part of this figure is Xi which at 4.4 I couldn’t see in the moonlight, but it stood out easily in the finder scope with no competing stars of similar brightness to confuse me.
Xi( ξ) serves as a guide to our second prize in the interior of Cepheus, the five-star multiple known as ΟΣ461. Now this was more challenging with plenty of nearby stars to confuse, but the beauty of it is this: It lies right on the same hour circle – almost to the second – as Xi ( ξ). So if you’ve found Xi, all you have to do is move due south a bit less than 5 degrees. (Which way is south? It depends on the time of year and night – but simply find Polaris. Look at the direction to Polaris and move in the opposite direction. Your finder probably provides a rough five degree fov to act as a guide as to how much.)
That’s the easy part. Now you need to be careful about the identification because I found at least one field that seemed to be the right one, but the star pattern I saw was simply too large. You need to be aware of what you are looking for – the chart below should help – and you need to be aware of the field of view of your eyepiece. (I was using one with close to half a degree field of view.) This whole group of stars fits in about four minutes – so that meant it would take up a little more than one-eighth of the diameter of my eyepiece field. Armed with that information, you can make short work of finding this. Without it, I spent quite a bit of time and frankly, part of what was confusing me was a little piece of text in the Haas book. But first take a look at this chart.
My problem is Haas says:
“The shape is pretty – three white stars in a straight line, all exactly alike, with a smaller star off to one side.”
When she says “exactly alike” I take it to mean roughly the same magnitude – and what jumped out at me were the stars I have labeled A, E, and X seem to fit this description – but “X” is not part of the combination, it just fits her description. You could say she means A, C, and E – but E is so faint (mag 10) that I had to look hard for it under these conditions and a 3 magnitude drop doesn’t fit the wording “exactly a like.”)
Bottom line – whether Haas confused “X” as part of the multiple star or not, I think other observers might – I did, going on her description. It wasn’t until I started examining my notes and comparing them to Starry Nights Pro screen – which is where the image comes from, as well as the distances and PAs – that I noticed the problem.
In any event, ΟΣ461 is worth a second visit on a moonless night. This multiple is attractive – and once I got over the confusion, I liked including “X” in this equation – “X” makes for an especially pretty grouping whether it belongs to the gang or not ;-)