[vsnet-chat 5968] Re: [AAVSO-DIS] CCD-V Vs visual observations

[Michael Koppelman <lolife@bitstream.net>]

I'm gonna go out on a limb here and say: CCD observations that have 
large errors are (most likely) systematic. That is, a reproducible 
event or error is involved, such as a bad comp star, bad image 
reduction, etc. In theory, if one makes a note of all related criteria, 
one can always re-reduce a CCD observation based on better information 
and revise the estimate accurately. CCD observations are, in this way, 
not subjective. You can screw up your process but it is hard to 
introduce subjective error.

Visual observations, on the other hand, rely solely on the experience 
and expertise of the observer and are much more subjective. The visual 
observer writes down how an estimate based on the way it looks to them 
at that moment. There could still be some systematic error, if a bad 
comp star is used, for example, but there is additional uncertainty 
based on the human being. You could go back and revise a visual 
estimate based on the systematic variables, such as comp stars, but you 
have a certain amount of uncertainty that is uncorrectable.

So if two CCD observers have very different measurements, you can 
probably figure out why. If two visual observers have two very 
different estimates, you *may* be able to figure out why, if a bad comp 
was used or something, but you may not. One human saw one thing and the 
other human saw another. There is no reproducible way to unravel the 
difference.

This is not to say that CCD observations are more accurate, but 
certainly in theory at least, the uncertainty is less subjective.

Michael Koppelman


On Sunday, February 9, 2003, at 06:15 PM, Sebastian Otero wrote:

> I would prefer my visual U Ori data a million times

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