[Aavso-photometry] TC Question

[Keith Graham]

Hi,



I have a question concerning transformation coefficients. I just completed a
3 night run of M67. I took 3 images each night through BVRI filters. I
averaged the 3 mag results for each filter for each night and then did TC
calculations for each night to see how they might differ from one another.
Two of the nights were pretty close, but the third night was quite different
(sometimes off by as much as .4). The conditions on that “off” night
included some high clouds. This made me think that we cannot possibly match
the conditions under which our TCs were taken to the any or all other
conditions under which data is collected. Since nightly conditions vary, how
can we be certain that the TCs we use will actually standardize the data for
any given night? Is there a method we need to be using to get the TCs as
close as possible to make them useful for any given situation?



Keith Graham