[vsnet-chat 4048] RE:Visual estimates accuracy

[reinder j bouma <rjbouma@wxs.nl>]

Sebastian Otero wrote:

> 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.

This last remark is really amazing to me!
If an observer wants to take full advantage of the capabilities of his
instrument,
and at the same time wants to produce consistant data, he should use a
SINGLE method.
Well, that can ONLY be achieved by using averted vision, because that
allows you to still see the faintest stars. To avoid 'color' effects of
bright stars, one should defocus the stars until no color is noticible
anymore. Only that way one is certain (more or less) that one is
observing in the same spectral bandpass (of the rods).
Rods are most sensitve at 520nm, while cones (as used in direct vision)
have their peak slightly redward near 560nm.
So mixing observations with both direct and averted vision is a bit like
mixing CCD-V with CCD-unfiltered data, and not saying so.
This is particularly obvious indeed in the R Lep data, but also in other
red stars like U and CH Cyg, where the 'direct' observations really
stand out as being far too bright..
Of course, (different) sequences and accidental errors contribute to the
scatter, but at least this methodology error is one that can be weeded
out easily.
So, always use averted (either in or out of focus) vision as Berto
already pointed out before, albeit in a more lenient way.
I think the other 'monsters' will agree.

Best regards,
              Reinder

By the way, at last the AAVSO has produced an new observing manual (to
replace a long out of print one of 1970 or so), in which this all will
be explained in detail (I assume, I have not seen it yet). Should be
highly recommended reading! 
--------------------------------------------------------------
Reinder J. Bouma    email: rjbouma@wxs.nl or rjbouma@planet.nl
Bekemaheerd 77      homepage: http://vsnet.shopplaza.nl/astro/
9737PR Groningen    
The Netherlands     phone: +31 (0)50-5418227
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