[vsnet-chat 192] Re: V vs v

[Fraser Farrell <fraserf@dove.net.au>]

G'day all,

On 1997-03-12 lagmonar@csir.co.za said:
   >importance of standardisation on v or on V for the magnitudes of
   >comparison stars used on charts for visual observers.
   >Maybe something to be added to the agenda for Sion before we
   >all start deriving 'wild' sequences from the Hipparchos pool of
   >data.

I would standardise on V, because it's reproducible and easy to
implement for electronic observing.  Although some stars may have
noticeably different V and v I think we just have to accept this
problem.  If the star is a tricky one, there are ways to calculate an
approximate v from the measured V and colour indices.

Choosing v as the standard immediately raises the issue of defining a
"standard retina" and its colour response.  Defining colour response is
particularly difficult because it will vary according to instrument
aperture and sky brightness.  Furthermore, there are psychological
factors at work - my pale blue star may look white to you, for example -
and the possibility of undiagnosed mild cases of colour blindness must
be considered.

Therefore, even if a formal definition of v is created; there will
_still_ be discrepancies for some stars between their "magnitude" and
what is visually perceived.  I reckon we should stay with V for "visual
magnitude".


cheers,

Fraser Farrell
Variable Stars Group
Astronomical Society of South Australia

WWW: http://vsnet.gist.net.au/assa/   email: fraserf@dove.net.au
traditional:  GPO Box 199, Adelaide, SA 5001, Australia

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