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Re: making stars

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  • Ed Lantz
    Another starfield bitmap available for purchase/license is Axel Mellinger s photographic all-sky panorama. It is available as an Aitoff projection in galactic
    Message 1 of 17 , Jan 15, 2006
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      Another starfield bitmap available for purchase/license is Axel
      Mellinger's photographic all-sky panorama. It is available as an Aitoff
      projection in galactic coordinates or as an equidistant azimuthal
      (polar) projection. The full resolution file size is 300 MB, allowing
      spherical zooming into starfield details without image degredation. The
      brightness of the Milky Way and other deep-sky objects seem to be
      exaggerated in this image, but since the mapping is very accurate, it is
      possible to exactly overlay a synthetic starfield and fade up Axel's
      image to provide an impressive Milky Way for an otherwise sterile
      synthetic night sky.

      Axel's photographic all-sky panorama is available at:

      http://home.arcor-online.de/axel.mellinger/

      He's also get a QTVR-like interface allowing you to pan the entire
      celestial sphere and zoom in on hotspot features at:

      http://canopus.physik.uni-potsdam.de/~axm/mwpan_vr.html

      And while you're on the site, check out Axel's other astrophotography
      at:

      http://canopus.physik.uni-potsdam.de/~axm/astrophot.html


      Ed Lantz
      Visual Bandwidth, Inc.
      Email: <mailto:ed@...> ed@...
      Web: <http://www.visualbandwidth.com> www.visualbandwidth.com
    • pedrosaantonio
      Hi! I must say that Ed Lantz is quit right. We have used this image and it is suberb. With some simple work you can extract the stars from the image, keeping
      Message 2 of 17 , Jan 16, 2006
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        Hi!

        I must say that Ed Lantz is quit right.
        We have used this image and it is suberb.
        With some simple work you can extract the stars from the image,
        keeping only the Milky Way background.

        The USNO has several star catalogues available, including the Tycho-2
        star catalogue of the 2.5 Million Brightest Stars (500Mb).
        http://ad.usno.navy.mil/star/

        Antonio Pedrosa
        Navegar Foundation
      • Ka Chun Yu
        ... Just be warned that because Axel mosaicked together many multiple shots of the sky, there are blend issues. The band of the Milky Way is pretty good for
        Message 3 of 17 , Jan 16, 2006
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          Ed Lantz wrote:
          > Another starfield bitmap available for purchase/license is Axel
          > Mellinger's photographic all-sky panorama.

          Just be warned that because Axel mosaicked together many multiple
          shots of the sky, there are blend issues. The band of the Milky Way
          is pretty good for the most part, but if you look closely at regions
          outside of it, you'll find "double" stars and other overlapping
          effects.

          Also if you try to overlay an exact starfield (e.g., the HIPPARCOS
          catalog) on the Mellinger image, you'll find many regions where the
          overlap is not perfect, and hence again the issue of "double" stars.
          Again, this is probably to the use of multiple, individual plates that
          had to be geometrically corrected and then tiled together to form the
          final all-sky panorama. These problems may not be an issue if you use
          a lower resolution version of the panorama, but if you have the full
          resolution, 300 MB-sized file, you'll notice it.

          (Also Axel may have fixed many of these problems in his subsequent
          tweaking of the mosaic. You'll have to ask him to know for sure.)

          Alternatively you can create an artificial, naked eye star field using
          the Bright Star Catalogue found at Paul Bourke's site, as suggested by
          Tom. For even more stars than HIPPARCOS (which has about 115,000
          usable stars), you can play with Tycho-2 (over 2.5 million), Hubble
          Guide Star Catalog (15 million stars), or the various USNO catalogs
          (the latest compilation with >1 billion collected objects, down to
          21st magnitude). However none of these have the diffuse features that
          define the Milky Way. (I thought once that if we plotted enough
          stars, some semblance of the galaxy's nebulosity would start showing
          up; I did it with the USNO-A2.0 (about 500 million stars) but even
          that many didn't give a very good looking result.)

          The big catalogs may also have artifacts around the bright stars,
          generated from the source finder algorithms that result in fake stars
          being counted. For instance I've often noticed that bright stars in
          the DSS plates will have their diffraction spikes, halos, and ghosts
          counted as multiple additional point sources. Also because the
          centers of bright stars are so blown out, their computed positions
          from the source detection algorithms might be off by more than a
          couple arcseconds.

          Here at Denver, we use HIPPARCOS (with different minimum luminosity
          cutoffs to set different absolute numbers of visible stars for our
          various needs) with the Mellinger all-sky. To nix the problem of
          doubles when overlaying artificial stars on the photographic panorama,
          we've removed all the stars from the Mellinger images using a cosmic
          ray detection and deletion tool.

          --kachun +** Dr. Ka Chun Yu **+
          +** Curator of Space Science **+
          +** Denver Museum of Nature & Science **+
          +** 2001 Colorado, Denver, CO 80205-5798 **+
          +** kcyu@... 303-370-6394 **+
        • Ryan Wyatt
          ... Actually, in our experience dealing with his version of about six months ago, we found very accurate alignment between Mellinger s image and our digital
          Message 4 of 17 , Jan 16, 2006
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            In reference to Axel Mellinger's all-sky, Ka-Chun wrote:

            > Just be warned that because Axel mosaicked together many multiple
            > shots of the sky, there are blend issues.

            Actually, in our experience dealing with his version of about six
            months ago, we found very accurate alignment between Mellinger's
            image and our digital database. We could drop the Digital Universe
            starfield on top of his image with near-perfect registration.

            > To nix the problem of doubles when overlaying artificial stars on
            > the photographic panorama, we've removed all the stars from the
            > Mellinger images using a cosmic ray detection and deletion tool.

            What tool did you use...? I only know of stuff that works on FITS
            images. And some of the stars are rather large (i.e., non-cosmic-ray-
            like), aren't they?


            Ryan, a.k.a.
            Ryan Wyatt, Science Visualizer
            Rose Center for Earth & Space
            American Museum of Natural History
            79th Street at Central Park West
            New York, NY 10024
            212.313.7903 vox
            212.313.7868 fax
          • Ka Chun Yu
            ... That sounds great. I guess he did get around to fixing those problems (our version of his panorama is at least 4 years old). ... Yes I did end up using
            Message 5 of 17 , Jan 16, 2006
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              Ryan Wyatt wrote:
              > In reference to Axel Mellinger's all-sky, Ka-Chun wrote:
              >> Just be warned that because Axel mosaicked together many multiple
              >> shots of the sky, there are blend issues.

              > Actually, in our experience dealing with his version of about six
              > months ago, we found very accurate alignment between Mellinger's image
              > and our digital database. We could drop the Digital Universe starfield
              > on top of his image with near-perfect registration.

              That sounds great. I guess he did get around to fixing those problems
              (our version of his panorama is at least 4 years old).

              >> To nix the problem of doubles when overlaying artificial stars on the
              >> photographic panorama, we've removed all the stars from the Mellinger
              >> images using a cosmic ray detection and deletion tool.

              > What tool did you use...? I only know of stuff that works on FITS
              > images. And some of the stars are rather large (i.e., non-cosmic-ray-
              > like), aren't they?

              Yes I did end up using tools for FITS images, specifically IRAF's
              cosmicrays package. It has options for changing the expected size of
              the cosmic ray, so with multiple passes, one can clean all the stars
              from the faintest to the largest (tens of pixels across) in diameter.
              One does have to decompose the 3-color image into individual color
              channels, save them out as FITS files, and then run them one at a time
              through the cosmic ray removal package.

              > Ryan, a.k.a.
              > Ryan Wyatt, Science Visualizer

              --kachun +** Dr. Ka Chun Yu **+
              +** Curator of Space Science **+
              +** Denver Museum of Nature & Science **+
              +** 2001 Colorado, Denver, CO 80205-5798 **+
              +** kcyu@... 303-370-6394 **+
            • Raymond Worthy
              To all Fulldomers or Dome-l members who sell projectors, The pace of development in this field is such that it is difficult to keep abreast of all that is
              Message 6 of 17 , Jun 21, 2006
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                To all Fulldomers
                or Dome-l members who sell projectors,

                The pace of development in this field is such that it is difficult to
                keep abreast of all that is happening, so I am taking this method of
                contacting you in one fell swoop.

                In the City of Newcastle in the north east of England, there is a well
                established museum called the Hancock Museum. The Hancock is being
                gutted and reshaped and will arise in a new existence and is to be
                called " The Great North Museum ".

                A London firm , Casson Mann (http://www.cassonmann.co.uk) has been
                engaged to see the project through The plans will include a seven metre
                planetarium and I have been asked to see if I can fit one of my fabric
                domes in.

                The scheme is to be finished some time in 2008, so there is a little
                time to think about things. If you have a digital projector which you
                think will be suitable for a seven metre dome, or if you are developing
                one which is scheduled to come on line next year, would you be so kind
                as to send the appropriate details to the following person, as well as
                to include me in the loop so I know what is going on.

                Adriana Ferlauto, adriana@...

                Yours faithfully,

                Ray Worthy.
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