[Aavso-photometry] Reality Check - Basic Concepts (Chart Magnitudes)

[David Trowbridge]

>> Question #3: Are the published values for Landolt standard magnitudes and
>> color indexes normalized for air mass = 1 (at the Zenith), or are they
air
>> mass = 0 (above the atmosphere)?
>> 
>air mass 0 (above the atmosphere).  This is always done for standardized
>photometry to remove all traces of atmospheric extinction.  Air mass = 1
>values for you will be different than air mass = 1 values for someone
>on Mauna Kea.

By extension then, I assume that the chart magnitudes (e.g., 1804-18 for
Nova V5558 Sgr) represent the same standardized photometry, corresponding to
air mass = 0. Right?

And what about visual magnitudes vs. V-filter magnitudes. Even though this
is not a CCD sequence chart (indicated magnitudes have only one decimal
point), can I still use it for getting V magnitudes?

(I guess I have some very basic issues to clear up!)


David Trowbridge