[vsnet-chat 1262] Re: H/T chart vs. VT mags...

[Taichi Kato <tkato>]

Re: [vsnet-chat 1259] Re: H/T chart vs. VT mags...

Fraser Farrell wrote:

> My guess would be light pollution.  I have noticed on many occasions how
> a starfield being observed will suddenly change character when my local
> football club finally turns off its floodlights!  There is a similar
> (but slower) effect when the Moon rises or sets.

   Another possibility may be, as pointed out elsewhere, attenuation of
blue light in Japanese atompshere.  There is a reported tendency that
Japanese observer(s) tend to report fainter magnitude for southern blue
stars (CVs).  I have confirmed the observer used (probably the same) V
magnitudes, and not GSC.  The atmosphere (as well as weather ;_;) over
Japan seems to be only too incoorperative.

> Perhaps the equation should read :
>  (visual mag) = V + 0.2(B-V) + (streetlight density factor)  ?  ;-)

   Perhaps the light polution term will be

  (visual mag) = V + k(B-V)

  where k = 0.2 - (streetlight density factor)
                - (atmospheric attenuation factor)
                - ...

   From my observing site (kyoto), k looks close to zero in moonless nights.
From super-urban sites (like Tokyo), k seems to be even negative...

> > I have heard comet observers use VT rather than V.  I would love to hear
> > comments from them also.
> 
> I know that Bill Bradfield uses V mags (from a variety of printed
> sources), because he doesn't have access to VT mags (or a computer).
> Justin Tilbrook works from the closest variable star sequence (usually V
> or SPv from VSS RASNZ).  I still use V to maintain consistency with my
> historical estimates.

   I have heard the ICQ has recommended (if I understand corrently from
indirect information) VT rather than V.  I hope this will not lead to further
inconsistencies between variable star and comet observers.

Regards,
Taichi Kato

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