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Thread: Attempt at resolving extremely close binary.

  1. #1
    Join Date
    Mar 2007
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    Falls Church, VA (near Washington, DC)
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    Attempt at resolving extremely close binary.

    I just now took a look at Eta Coronae Borealis with my Celestron 8. I went for broke and pushed the magnification to 625x, giving about the same Airy disk image scale as reported observations with the Lick 36" refractor at 2,600x. In moments of good seeing the star looked slightly elongated while a nearby single star looked perfectly round. I must admit that since I already knew the position angle from a chart, I cannot totally rule out confirmation bias. According to that chart in Sky Catalogue 2000.0, Vol. 2, the current separation is about 0.35 arcsecond, somewhat under Dawes' limit for an 8-inch scope. The central obstruction actually helps with nearly equal pairs by reducing the diameter of the central spot in the diffraction pattern.

  2. #2
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    Addendum: This attempt reminded me of what I read about attempts at resolving Capella with the Lick refractor over a century ago.

    This battered 44-year-old telescope continues to give good star images, despite a 3-foot fall onto a concrete slab a few years ago. That resulted in a dent in the edge of the corrector cell, but no optical damage. It needed only a minor collimation touch-up of the secondary mirror. It made me chuckle at how a competitor belittled the Schmidt-Cass as a design that can easily lose its collimation. Celestron built them rugged in 1976.

  3. #3
    Join Date
    Oct 2011
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    Fresno, CA
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    That's excellent. I've never attempted anything quite so close.

    According to my records, which I keep in SkyTools, I have completely split Tegman (Zeta 1 Cnc) and Xi Sco, both at 1.1" separation, using both my 8" and 11" SCTs. My favorite eyepiece in both scopes is the Televue 13-mm Ethos, which gives 156x in the 8" and 215x in the 11". I also have 8-mm and 5-mm eyepieces (the latter giving 560x in 11'), but I use these mostly on the Moon and planets. With the 5-mm eyepiece in the 11", I have seen the hexagon around Saturn's north pole several times.

    I also have a 5" SCT, but back when I was using it a lot for visual observing I didn't look at a lot of double stars. The best I have done with the 5" is Eps 1 & 2 Lyr (the Double-Double), each at 2.5" separation.

    Until a few minutes ago, my observing plan for this weekend included 3 planets, 3 comets, 4 asteroids, a dozen carbon stars, dozens of galaxies and globulars ('tis the season), a dozen nebulae, but just 5 double stars. (My observing plans are always bigger than I can get through in one evening.) But, after reading this I added ten doubles with separations between 0.5" and 1.0". Hopefully, the skies above Kings Canyon National Park will cooperate.

  4. #4
    Join Date
    Oct 2011
    Location
    Fresno, CA
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    48
    No luck on the tighter doubles last night. Transparency was very good, but seeing was variable, sometimes calm and sometimes shaky. I split Xi Sco easily, but that was during a moment of calm. I tried a few tighter doubles, but the best I could get was an oblong star. One problem is that I usual observe stars before the sky is completely dark, when I then switch to things like galaxies, nebulae, comets (I snagged two of the three of was after). During this window of opportunity, the skies are often turbulent. After about 10 p.m., the skies were pretty much rock solid, but I wasn't doing stars.

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