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23/08/02 |
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mean difficulty |
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do not miss it! |
Gear: Antique 1903 4-1/2” [~115mm] f/15 Brashear refractor (which made the cover of August Sky & Tele), hand driven EQ; Baader prism diagonal and Baader Hyperion 8-24 Zoom, plus a Televue 3-6 Zoom. This is a lovely kit for easy visual observing. Zoom eyepieces make double star viewing a real pleasure as you can get to the correct magnification very quickly without swapping a lot of eyepieces. The Baader zoom is exquisite with its wide field and superb optics. Its single drawback is that it is not parfocal. The Televue is almost perfectly parfocal, but its field of view is considerably narrower. It also has outstanding optics. Between the two, it gives me a range of magnification from 71X to 572X! The practical limit for the Brashear is 450X so I was covered for all seeing conditions. Oh, and I use an adjustable observing chair. Comfort is paramount.
Site: My backyard in Forest Hills, Queens, NYC. Bortle 10 (ughh!) and surrounded by 3 story houses, but a clear horizon from about 25 degrees and higher in the East and South. “It’s complicated.”
Conditions: 70F/21C, holding steady. 58% humidity, -0- clouds, -0- wind, transparency est. 7/10 (lightly hazy with a halo easily seen around the moon. The 97% waning moon was initially behind the neighbor’s house but rose into full view at 17deg 30min around 23:15 local time. Seeing (spoiler alert 9.5/10).
Observation:
Mu1 Cyg, 23:10-23:20 local time. It was perfectly placed at +55○ altitude. At Mag 4.49 (some listings have it at mag 4.6, but that is only the primary), it is too faint for me to see naked eye in the glow of NYC. But it shows up easily enough in my little finder, and it was easy to identify as it has a bright-ish nearby star, HIP107326 at mag 6.85. Centering on the brighter of the two stars in the finder, Mu1 Cyg was in the field of view of the Hyperion zoom at low power. I immediately dialed it down to 8mm, 214X and noticed that it was elongated. OK, found it! And the seeing looked encouraging. Swapping in the Televue 3-6 Zoom, at 6mm (286X), the double now separated cleanly. And it was rock-steady in the eyepiece. The primary’s Airy disk was sharp. One diffraction ring was visible in the light pollution/moon glow/light haze background. But the B component was clearly visible and well separated. The separation is listed as 1.51 in Stelle Doppie, but digging deeper, it was last measured in 2019 by Izmailov and the current Washington Double Star orb6 ephemeris lists it at 1.472 arcseconds for 2023, with a quality degree of 3, which is pretty good.* What makes this a tricky double is that the B component is sitting smack in the diffraction ring. I dialed the eyepiece to 5mm (343X) and clearly saw this. I also noticed that both Airy disks were still hard edged and dead steady. The seeing was superb and the Brashear lens had reached perfect thermal equalization with the unchanging temperature. I got the sense that this was a rare night. It is not often that I’m tempted to increase the magnification to 429X, using the 4mm setting, but last night the seeing held up and the view of this double was sublime. The color of the mag 4.69 primary Airy disk showed a very distinct pale creamy tinge and the fainter mag 6.12 secondary was a definite blue-gray. The seeing was so good that the diffraction ring was complete all around, not breaking up, and uniformly bright. The distinct impression was of a diamond ring surrounding the primary disk, with the secondary being the jewel. Amazing! |
