Mu (μ) Draconis (Alrakis)
RA: 17h 05m Dec: +54° 28′
Mag: 5.7, 5.7 Sep: 2.3″ PA: 14°
Dist: 88 ly
Spectral Classification: F7
I love this pair! They looked like a couple of bowling balls rolling down my field of view and being perfectly matched they are a very close version of the beautiful binocular double, Nu (ν) Draconis. What’s more, there was a nice lesson in here for me, since I compared my experience with them with my experience with Epsilon (ε) Draconis. And the day after I posted this I discovered the Dragon has yet a third sat of eyes! They are 16-17 Draconis and I’ll treat them in a separate post.
What I found with Epsilon(ε) was that even though they were wider apart – 3.2 seconds for Epsilon (ε) vs. 2.3 for Mu (μ) – I could split the closer pair, Mu(μ), easily with the 76mm – and Sissy Haas says its easy with a 60mm! – and yet I needed the 127mm scope to split Epsilon (ε)! Why? Because of the difference in magnitude between primary and secondary. Now this is really not news to an experienced double star observer – but it’s always nice to see theory borne out in practice. With Epsilon (ε) you get a difference of almost three magnitudes – with Mu (μ) there is simply no difference! Stars of the same brightness are much easier to split than stars where the primary is brighter than the secondary.
Finding Mu (μ) presented a challenge for me because I had a nearly full moon behind me. I could not spot Mu (μ) with my naked eye. In fact, I couldn’t spot Nu (ν) – at 4.9 nearly a full magnitude brighter – with my naked eye, but because it’s the dimmest corner of the Dragon’s head it’s relatively easy to find – and it’s absolutely unmistakable in binoculars or a small finder – two 4.9 magnitude stars split by 63.4″ – a full minute and then some. So Nu (ν) was my jumping off point to Mu (μ). Sort of like going from daddy dragon to baby dragon! It also happens to be almost on the same declination circle as Mu (μ)- Mu (μ) is at 54°28′ and Nu (ν) is at 55°11′. So I got Mu (μ) in view with my widest eyepiece – about a degree – and shifted it over to the north side of that eyepiece. I then locked the declination axis on the equatorial mount and panned in right ascension until a bright star came into view – that’s a short trip as well because Nu (ν) is at RA 17h 32m and Mu (μ) is at 17h 5m. I popped in a 10.2mm eyepiece and could see I had a double – but unsplit. So i went to the 6-2 Nagler zoom. At 6mm (200X) it split – at the 5mm click stop (240X) it was even better.
Now Haas says “They are just bright enough to be easy with a 60mm.” On a better night I’ll put that to the test. She also says they “are almost fully split with 120X.” Uh huh. So what exactly did she split it with? Because 120X is really pushing the limits of a 60mm scope. I guess I’m really not sure what “almost fully split” means? For me, “split” means so you can see dark sky between the stars.Anything less than that isn’t a split. So now I’m really curious about giving this a go with a 60mm. Meanwhile, I took a break in writing this report to do a little observing with a 100mm F6 Orion – and I tested it’s optics on Mu which was getting fairly low in the west – and I split it. Good optics for an inexpensive and pretty fast (f6) achro! I think I’ll be coming back to this pair frequently.
(Bonus – if you don’t know your Greek alphabet yet, just reread the paragraphs above – no matter how long I deal with them, Mu (μ) and Nu (ν) haunt me. But I may have gottenthe confusion out of my system by writing this – or made it worse. 🙂