[vsnet-chat 4043] Visual estimates accuracy

["Sebastian Otero" <varsao@fullzero.com.ar>]

Dear Taichi:
                 I was writing a collaboration with Stan Walker about
accuracy in visual estimates and  found this:

OMICRON CETI:

>   20010105.419    67  (T. Kato)
>   20010110.387    69  (T. Kato)
>   20010111.528    69  (T. Kato)
>   20010112.000    67  (S. Otero)
>   20010112.385    70  (T. Kato)
>   20010113.000    66  (S. Otero)
>   20010113.560    69  (T. Kato)
>   20010114.383    69  (T. Kato)
>   20010115.000    67  (S. Otero)
>   20010115.428    70  (T. Kato)
>   20010116.394    70  (T. Kato)

Actually, we independently caught a 0.1 magnitude rebrightening on January
13th. (the 0.3 mag. difference between our numbers is probably due to a
chart thing. I use V magnitudes and the AAVSO chart stars are  0.2-0.3 mag
fainter. Are you using that chart or is it just a color-sensitivity
problem?)
"Overobserving" can be very useful if we observe carefully.

My articles are all about the technics used in visually vsoing, specially
when we observe stars of different colors.
My point is that a subtle change in HOW we observe the stars may be
reflected in several tenths of a magnitude discrepancies.
"HOW" means if we used averted, parafoveal (intermediate type, se Hallett,
1998, JAAVSO vol 26, 139) or direct vision.
If we are not aware of these different responses of the eye and randomly
observe with one vision or another, without taking care, results may be
dissapointing, specially for stars like R Lep, that are very red and may
completely disappear if we used averted vision for observing them. (I've
noticed 1.4 mag. differences for that star, which is saying we are observing
it in different ways).

If Stan agrees I will send a copy or parts of the article to vsnet-preprint
or vsnet-chat. And I think it would be interesting to exchange our technics
and experiences on this matter.
I believe that most of the discrepancies can be explained easily by the
different types of vision used.
And now that Johnson V is being accepted as a standard for visual
comparisons and charts are being converted to that system, I think observing
technics ought to be revised.
Furthermore, most of the charts that supposedly show "v" magnitudes have
values that are a mix between V and v.

I've realized that most observers use averted vision for all their
estimates. That would mean that red stars are always fainter in telescopic
estimates. And blue stars are always brighter.
If stars are not the same color and if it's not made for detection at the
limitting magnitude, I always try to avoid averted vision for all those
problems.

I wait for comments from all observers. It would be great to hear what
technics are used by Monard, Stubbings, Granslo, Comello, Pearce and all
that "mosters" (;-)) that report to vsnet.

Cheers for all,
Sebastian.




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