[Aavso-photometry] Basis of magnitude system

[Brad Walter]

According to Henden & Kaitchuck in Astronomical Photometry,  the UBV
system is defined by 6 AOV stars: Alpha Lyr, Gamma UMa, 109 Vir, alpha
Crb gamma Oph, and HR 3314. The average (B-V) and (U-B) of these stars
is defined to be zero

(U-B)average = (B-V)average = 0

-----Original Message-----
From: aavso-photometry-bounces at mira.aavso.org
[mailto:aavso-photometry-bounces at mira.aavso.org
<mailto:aavso-photometry-bounces at mira.aavso.org> ] On Behalf Of Peter
Nelson
Sent: Monday, January 23, 2006 4:19 AM
To: aavso-photometry at aavso.org
Subject: [Aavso-photometry] Basis of magnitude system

A random question:  All magnitudes are relative and there must be a
defined standard(s).  I am aware of the North Polar Sequence, and
Morgans UBV standards.  How were these standards devised?  Was there an
AO star which was defined as magnitude x and B-V=0 from which all other
standards were
carefully measured?  

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