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  1. #1
    Brian Tung's Avatar
    Brian Tung Guest

    Default Opus Observes: Back in the Spring of Things



    It's been a while since I posted one of these things.

    2:50 a.m. 25 April 2004 PDT (2004-04-25-0950 UT)

    That date is not a typo. My time outside with Opus has been limited
    quite a bit lately, mostly because of the kids, but also because the
    usual California "June Gloom" came by a few months early this year.
    But that seems to have passed us by for the moment (knock on wood,
    plastic, multi-coated optics, anything I can get my hands on). I had
    to sit with the younger one to get him to go to bed, and unfortunately,
    his bed is so comfortable that I went ahead and fell asleep, too.

    It was about 2:15 before I woke up again. I immediately considered
    going out for a session, but I wasn't sure my body was up to it. I
    read my e-mail and news as a temporizing measure, and by the time I
    finished (putting in a fairly lengthy post, as I recall), I was
    sufficiently energized to dig out the stuff.

    It really has been a while. The last time I had actually observed
    with the C5+ was about September, when I did an experiment with
    simulated spider vanes, testing the effects of diffraction. Since
    then, I had been out with the Wocket (Tele Vue Ranger) and Snuffy
    (Starsplitter 10-inch truss dob), but never with Opus. Actually,
    that isn't literally true, but the only times Opus had been out was
    during the day, when I attached the Wocket plus H-alpha filter to the
    Opus's photo bracket for tracking purposes. I hadn't actually looked
    through Opus at any time.

    Well, that was about to change. I now leave the telescope entirely
    set up in the garage (cleared out enough space for that, at least),
    and all I have to do is pull it out to the patio, get my chair, take
    off the four covers (front and rear of the scope, front and rear of
    the finder), slip in an eyepiece (32 mm Plossl to start with), and
    I'm off. I didn't bring an atlas or planisphere; as is my usual
    tactic now, I just bring my Palm, and do all my star-hopping from
    there.

    My first target for the night was M27, the Dumbbell Nebula. I didn't
    spend much time with it at first, just wanted to make sure I could
    still find the darned thing. It's a sign of how late I was up that
    this object was already reasonably high up in the sky. I decided I'd
    come back for this later, and went on to M57, which I also just took
    a quick glance at.

    Then to M4, the famous globular near Antares, in Scorpius. I think
    it's pretty amazing that I once couldn't see this at all (possibly
    under better conditions, but it's hard to compare); not only can
    I see it now, but even from home, the well-known north-south bar is
    fairly easily visible. What's more, I can tell that the bar is a bit
    off north-south--more like a bit north-northeast to south-southwest.

    At this point, I decided to put in my reducer/corrector, which I had
    left off during last year's Mars apparition. My first target with the
    reducer in was Stock 1, a large, sparse open cluster close by Albireo.
    Under moderate light pollution (to my eyes, the ZLM was about 4.7),
    this cluster is only somewhat detached from the background stars,
    with a slight density gradient toward the center, where there are some
    10 to 15 stars of magnitude 8 or 9 arranged in a thick V pointed toward
    the east. Later, I tried this cluster with the 10x30 binoculars, and
    it's definitely more attractive through those.

    A bit more interesting is NGC 6823, a medium-rich open cluster about
    2.5 degrees to the southeast of Stock 1. It's much smaller, and has
    only three or four stars that are easily visible, but I kept getting
    the sensation of a secondary layer of stars in the 11th-magnitude range,
    or maybe a little dimmer, lingering just beyond. I didn't verify that,
    since I would have needed to bring out Snuffy for that, and I didn't
    have the energy for that.

    I also tried, without much expectation for success, for NGC 6820. This
    nebula has long thought to have been identified with a large arc of
    gas and dust in which NGC 6823 is embedded, but as Bill Ferris has
    noted, the NGC description does not match this object. It seems better
    aligned with a small reflection or emission nebula about a quarter
    degree to the southwest of the open cluster. This object was definitely
    invisible to me without a narrowband filter. With the filter, there
    might just possibly have been somethere visible there, but I certainly
    couldn't say for sure. I'll have to write it down as a negative
    observation.

    I tied up the session with a glance at M11. The Wild Duck Cluster was
    then in the southeastern sky, which is still well within the light dome
    cast by Los Angeles--even at that time of night. But I was able to find
    lambda Aquilae, and then through the finder, it's a simple star-hop
    around a small crown-like asterism joining lambda to the northern stars
    of Scutum, and lying in wait at one corner of the crown is M11. The
    cluster takes magnification well in a small telescope, and I could best
    see the cluster at around 100x or so, the eighth-magnitude star sitting
    just off the corner of the square-edged fan.

    After packing up the telescope, I came outside with the binoculars and
    looked up (besides Stock 1) Albireo and M27. I forget how enjoyable a
    way it is to relax and look up in the sky while sitting comfortably.

    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  2. #2
    Axel's Avatar
    Axel Guest

    Default Opus Observes: Back in the Spring of Things

    > Then to M4, the famous globular near Antares, in Scorpius. I think

    I remember one evening three years ago, with no moon in suburban
    Houston, that I couldn't see M4 at all through my 8" Dob. Light
    pollution really kills this one. Whereas an inherently much brighter
    GC, like M13, shows up much easier in light pollution despite the
    greater distance.


    My notes for this one (through a 12" SCT) indicate a core of four or
    five bright members, then a gap or sort of "moat", and surrounded by
    an encircling ring of many more fainter members. The ring sounds like
    your "secondary layer of stars."


    During the same session we tried for the faint nebula NGC 6820 atop
    and around this cluster. My two friends claimed to have seen it, but
    I couldn't back them up...

    Nice report, thanks.

    Ritesh

 

 

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