[Aavso-photometry] Differential vs. absolute magnitudes - Extended Format

[Tim Crawford]

Gianluca,

Regarding the new AAVSO extended Format (and CCD
individual obs, for that matter) the terms
differential (DIF) and absolute (ABS), in themselves
have no direct relationship to transformation
coefficients or all sky photometry (please keep in
mind that observations can be either transformed or
not transformed for either the DIF Obs or the ABS
obs).

Have you studied the extended format description; if
you study it and the examples you should be able to
figure out some of the differences:

www.aavso.org/observing/submit/extended.shtml

A lot of us are not real happy with the name choices
(DIF & ABS) as used now for the extended format (and
also is present as an option with the individual CCD
obs) because of the confusion they create with how the
majority of us have used the term differential
photometry in the past.

1)  Both the DIF and the ABS options are simply the
same differential photometry that we have been and
continue to do but whose final results are presented
differently.

2)  The difference now is that ABS Magnitude denotes
our traditional differential photometry: (v-c) + C =
V.  Keep in mind that lower case letters represent
instrumental mags!

DIF Magnitude denotes only the differential photometry
v-c values (not unlike how the CBA gathers it's data),
as near as I can tell; although the "math" does not
really work with the #4 example on the web page.

3)  Please note that DIF is currently NOT RECOMMENDED
as an option so should not really be creating any
concern.

4)  Just keep in mind that Absolute (ABS) is in fact
the same differential photometry that we have all been
doing... just another label to adjust to.... 'taint no
thang

Per Ardua ad Astra

Tim Crawford CTX
Arch Cape Oregon