Re: [vsnet-chat 6006] Re: [AAVSO-DIS] Re: v1413 Aql - Ready for Eclipse > This is not possible. Studies have shown that a minimum of 90 quanta > incident upon the fully dark adapted human eye is the threshold of > detectability (with optimum target size and flash duration). These values may be dependent on experiments. I know there exist physiological description that the threshold is much lower, even corresponding to a few detected photons in a single retinal cell. > This corresponds to a magnitude of 7.6 for a Vega type star just detectable > with a fully wide 7mm iris. Which becomes magnitude 13.4 for a 4" > aperture. Won't observers be surprised to hear this limiting magnitude for a 10 cm (4 inch) aperture? I had years-long experience with this aperture, but the limiting magnitude 13.5 was a "usually detectable" value under moderate conditions (in moderate citylight). I once had an experience to catch the outburst of EY Cyg in rise. According to the reports to the AAVSO, the object was recorded below 14.0 (in average) on the same night. I remember that the object looked "conspicuously brighter than usual". The quoated value more looks like to me a safe limit. > About 10% of those actually get through to be detected by the rod cells, > so in fact statistically even less than 1 quanta is getting "detected"! In what time, in 1 second? The time-constant of the eye response may not be always 1 sec or similar length. Furthermore, there is always Poissonian fluctuations of photon detections. It is possible, even at this mean photon rate, one may detect a packet arrival of photons in a reasonable waiting time. The observer may have succeeded in training the detection neural network to distinguish the increased occcurence of such events against the background. Regards, Taichi Kato
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