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Re: (meteorobs) More on LM estimates and sources of error in ZHRs
Lew Gramer wrote:
>
> >I recall, from my early biology classes, that the human dark-adapted
> >retinal rod cells, are extremely efficient in responding to just a few
> >photons to yield a detectable response. If the average rod cells, at
> >their limit, respond to a few photons at mag 6.5, how can a rod cell
> >respond to 1/9 as many photons (which is the luminosity ratio for the
> >8.9-6.5 = 2.4 mag difference here) , because that many photons just are
> >not going to be there ?
>
> Mike, I think it would be difficult to argue that the photons are "not there"
> based on an a priori assumption that response at 6.5 is "at the limit", wouldn't
> it?
Not really. If I recall my biology lecture correctly, it takes a few,
(maybe 1,2 or 3)? photons to register the minimal detectable signal on a
rod cell. Now, since a 6.5 star (barely detectable for the average eye)
would be sending just a few photons to the rod cell, my point is, how
could an 8.9 mag star be detectable if it sends only (few)/9 ~ (1 or
3)/9 = 1/9 or 1/3 photon? That seems to be below the threshold of
response.
>Anyway, I think as George said, we're no longer discussing human >perception
> here: what this sounds far more like is, "*I* have excellent night vision, and
> *I* have access to excellent dark sites, and *I* have never seen mag 7 stars (or
> mag 8, or what have you) - and therefore, it is impossible...
Not at all. I was analyzing the claim of an 8.9 limiting magnitude,
which is an order of magnitude fainter than what is generally the
average limit for most people. I believe people with particularly good
night vision can break 7.0, certainly.
> I hope this won't offend ANYONE, but I am quite clear that I am able to see
> stars fainter than mag 7.5 under appropriate conditions. If that is something
> specific to my vision (or anyone else's), that's OK - so LONG as I accurately
> record my conditions, so my meteor (or nova, extragalactic supernova, variable
> or whatever) data can be reliably corrected for that individual variation.
>
> That's basically the whole gist of Limiting Magnitude: what can THIS individual
> see, and how will that affect their reported observations...
>
I was attempting to analyze this from a physiological point of view, and
trying to show that the extreme limiting magnitudes reported before, may
not be physically possible? I agree that individual perceptions will
vary, and that the people who can see mag 7.0+ likely have a good
combination of extra sensitive rods and larger than normal pupils. But I
don't believe a human could detect mag 8.9, an order of magnitude
fainter than the normal limit, which is why I wanted to study the
"double-blind" studies in detail.
Mike.
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