Re:Limiting Magnitude

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Posted by Richard Miles at 18:24 on 2013 Dec 09

Just one final point, Eliot. You write:"Using a bigger aperture or a more sensitive camera will only decrease the time to which you get to the sky’s limiting magnitude (however shorter exposures are useful for faster moving objects)."The sky will have a certain brightness (usually in the range for a dark sky of magnitude 19.5-21.5 per square arcsecond – V mag equivalent). So imagine the seeing and sky brightness are fixed then the bigger the aperture, the greater the signal to noise and so the fainter the limiting magnitude. N.B. The plate limiting magnitude is often stated to be an SNR of 2.5.If my memory serves me correctly, the faintest object I have reported astrometry of using a Celestron 11 is V=21.5. I stacked quite a few images for that!Cheers,Richard