[vsnet-chat 4335] Visual estimates

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

> Taichi Kato wrote:
> >
> > > When trying to interpret a star's behavior based on visual data,
> > > there is inevitably going to be uncertainty involved. There is
> > > usually about a magnitude of scatter in visual observations

>    Does the 1-mag scatter cited refer to the scatter between different
> observers?  The standard deviation for the "average observer" is
> around 0.2 magnitude I recall, and I have seen what appear to be
> consistent zero-point differences between different visual observers.
> It sill amazes me that some observers are able to estimate to a
> precision of less than 0.1 magnitude.  I don't consider myself a
> particularly good estimator, but my observations of standard are
> very consistent (around +/- 0.03 mag., standard deviation) over
> relatively short time intervals during one night.


If the problem was just people's color response or if we can apply an offset
of 0.5, 0.2 or whatever magnitudes then the work will be okay. That would be
an awaited piece of "evaluated data". But I've been comparing observations
and noticed that when a star is rising for one observer, sometimes is fading
for other.
I have seen my observations of a red star at 6.0 the same day another
observer reports a 6.6 and two months later I have reported a 6.2 and the
same observer is watrching the star at 5.9 !!!
There is something more than a colour term. Techniques are very important.
And checking and preactices too!!!



>    Analogous transformation equations for visual observations would
> undoubtedly vary from observer to observer and night to night (and,
> in my own case, seemingly from hour to hour!).  There may be
> value in transforming visual observations in a similar way.  They
> _could_ be corrected for differential extinction, based on
> observations of standard stars (perhaps using the M-67 project
> methodology, or some variant of it) at various zenith distances
> during the night.
>
>    That doesn't necessarily require a lot of additional observing
> time, but perhaps too much for what is an unclear gained from it
> all.  Experiments with my own observations have not been very
> conclusive - nor very extensive either, I admit!
>

As a visual observer I don't do variable star estimates when I think the
degree of accuracy has dropped behind the 0.2 mag. limit. So the stars I
observe tend to be at higher altitudes. That's why alpha Ori, eta Gem, mu
Gem, etc. are over for me this season.
If I report them I would be lying or reporting probably erroneus data that
it is not worth. That is from my polluted Buenos Aires skies...:-((

Regarding extinction I agree with Stan: for instance, here the south is
white because of the outskirts indistries. the north is darker because it is
where the R$ByP(B de la Plata is. Conditions change continuously.
I prefer not to make uncertain observations (but when I do, I put a ":")
So I haven't needed any correction to get a good value.

Cheers,
Sebastian.

PS:  I'm doing something on DE Dra. Nothing seem to fit with Hipparcos PA
lack of eclipses. I'm starting to think the eclipses are spurious. Kari's
observations are probably the only clue.







---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://vsnet.grisoft.com).
Version: 6.0.249 / Virus Database: 122 - Release Date: 14/04/01

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp