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Space Forum / Amateur Astronomy / July 2008magnitude and averted vision
Is visual magnitude based on what you can maximumly see with averted vision? Last night the stars below Beta and Upsilon Lyra only appeared with averted vision. I concluded the sky was mag 5.5 with below average seeing. (there was scintillation for lower horizon stars). >Is visual magnitude based on what you can maximumly see with averted vision? > [quoted text clipped - 3 lines] >scintillation for lower >horizon stars). Hi Mike- I suspect you mean _limiting_ visual magnitude. Visual magnitude itself is the same, regardless of conditions or how you actually observe. I always judge limiting visual magnitude on what I can see with averted vision. You're interested in the dimmest thing you can perceive, by whatever method you find most effective- averted vision, tapping your eyeball, whatever. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com > Is visual magnitude based on what you can maximumly see with averted vision? It's like Chris said. It's generally referred to as "Naked Eye Limiting Magnitude" and usually abbreviated as "NELM"; and yes, its the faintest star you can 'just' positively detect using averted vision. Bill Greer To sketch is to see. http://cejour.blogspot.com http://www.rangeweb.net/~sketcher On Jul 31, 1:58 am, "Mike Thomas" <M...@nospam.net> wrote: > Is visual magnitude based on what you can maximumly see with averted > vision? It's like Chris said. It's generally referred to as "Naked Eye Limiting Magnitude" and usually abbreviated as "NELM"; and yes, its the faintest star you can 'just' positively detect using averted vision. Ok ! It's too bad transparency and seeing don't go hand in hand. From my backyard on the outskirts of Calgary, having both great seeing and good transparency rarely meshes. Oh also the 2 stars in question where lambda and nu(2) Lyr > Is visual magnitude based on what you can maximumly see with averted > vision? It's like Chris said. It's generally referred to as "Naked Eye Limiting Magnitude" and usually abbreviated as "NELM"; and yes, its the faintest star you can 'just' positively detect using averted vision. > Is visual magnitude based on what you can maximumly see with averted vision? "The LM [limiting magnitude] is usually defined as being equal to the brightness fo the faintest star just visible to the slightly-averted, fully dark-adapted, unaided eye." McBeath, A. 1991. Visual limiting magnitude determination charts. 1991JBAA..101..213M http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1991JBAA..101..213M - Canopus56 P.S. - My resource page on finding NELM (naked-eye limiting magnitdue), ZLM (zenithal limiting magnitude) and TLM (telescopic limiting magnitude) http://members.csolutions.net/fisherka/astronote/plan/tlmnelm/LimitMagFields.htm |
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