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Contains:  NGC 6645
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Barnard's dark nebulae B312 and B313, 





    
        

            Duczmal
Barnard's dark nebulae B312 and B313

Barnard's dark nebulae B312 and B313

Technical card

Resolution: 4516x3614

Dates:June 24, 2017

Frames: 44x300"

Integration: 3.7 hours

Avg. Moon age: 0.45 days

Avg. Moon phase: 0.23%

Astrometry.net job: 1982003

RA center: 278.342 degrees

DEC center: -16.009 degrees

Pixel scale: 2.326 arcsec/pixel

Orientation: 1.513 degrees

Field radius: 1.869 degrees

Data source: Traveller

Description

This region, on the border of the constellations Scutum/Sagittarius, contains two dark nebulae, B312 and B313 (at left), from Barnard's Catalogue of 349 Dark Objects in the Sky. It also contains the open clusters NGC 6645 and Ru 171.

The catalogue was based on Barnard's pioneering work "A Photographic Atlas of Selected Regions of the Milky Way" (Barnard E. E., ed. Frost E.B. and Calvert M.R., Carnegie Institution of Washington, 1927). Barnard used the Bruce telescope to photograph the Milky Way from Mount Wilson, California, in 1905, which was described by himself:

"The materials employed were specially chosen for their transparency – the flint being very light and the crown very white. The focal lengths of the front and rear combinations are in a ratio of about 7 to 12, while the focal length of the system is very nearly five times the aperture. The focal length you may find very slightly modified; indeed, it is our custom to balance the inevitable zonal differences of magnification to all constructors of astronomical objectives. The focus of the 10–inch, determined from the photographs, is 50.3 inches (127.8 cm), and the scale is therefore 1 inch = 1°14 or 1° = 0.88 inch. The ratio, a/f = 1/5.03, I believe to be the best for the purpose. The accumulation of interest had by this time permitted the purchase of a 6 ½–inch Voigtlander lens of 30.9 inches (78.5 cm) focus, which had been in commercial use. As indicated, the telescope is really triple in character, there being three tubes bound rigidly together on the same mounting – the 5–inch visual telescope for guiding, and the 10–inch and 6 1/4 –inch photographic doublets. For each of the photographic lenses there is an inner tube, with focusing scale, which can be racked back and forth for the adjustment of focus. There is considerable change of focus in the 10–inch lens between winter and summer. The change in the focus of the 6–inch is small, however, and requires very little correction. The plate–holder for the ten–inch carries a plate 12 inches square, while the one for the 6 ¼ –inch carries a plate 8×10 inches." (http://www.astrosurf.com/re/atlas_barnard_1927.pdf).

My thanks go to João de Barros and the SONEAR team.

Comments

Author

cosmophoton
Duczmal
License: Attribution-NonCommercial-ShareAlike Creative Commons
3474
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Revisions

  • Barnard's dark nebulae B312 and B313, 





    
        

            Duczmal
    Original
  • Barnard's dark nebulae B312 and B313, 





    
        

            Duczmal
    B
  • Final
    Barnard's dark nebulae B312 and B313, 





    
        

            Duczmal
    C

Sky plot

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Histogram

Barnard's dark nebulae B312 and B313, 





    
        

            Duczmal

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