Teams / The Mark I Eyeball Team / A couple of questions to start things rolling.

A couple of questions to start things rolling.

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Hello,I have just posted a response to a question on the Visual Observing Forum, 'Avoiding Bias: a Few More Rules for Variable Star Observers'. Alex Burda suggests that the use of comparison star magnitudes as labels, as on AAVSO charts, might bias results in some way. British Astronomical Association Variable Star Section charts which I use label stars with letters, and only list their apparent magnitudes at the bottom of the chart. This isn't something I have thought about before, but lacking any evidence either way I'm inclined to agree with Alex. What do others think?Secondly, the BAA chart for eps Aur gives comparisons closer in apparent magnitude to eps Aur than does the AAVSO chart, but further away on the sky (eg eps Per differs in RA by about an hour). What might be the different errors introduced by these two factors?David.

Comparison stars labels

Hi, David,In my experience, knowing the magnitudes of the comp stars helps. That fact has to do with the technique I use. Every time I observe a variable star I intuitively check the comparison stars. Everyone has to do that actually in order to find the two right ones to use. By doing so I examine that the magnitude difference between them is perceived okay. Knowing that there is, for instance, a 0.13 mag. difference between A and B and a 0.26 mag. difference between B and C is useful to calibrate the actual estimate of the variable star afterwards. I check 3 or 4 of the comp stars magnitudes to choose the two that will be used to make the estimate. Also checking the actual magnitudes you may find some discrepance in their brightness (chart problem or even... a new variable star!)When you have a more or less fixed program (as I do) you end up knowing all the comp stars values by hard. I don't use charts actually... So the whole issue doesn't apply anymore.About the distance to the comp star, well, you can't have everything... I think it is probably up to the observer and what he/she feels more comfortable.Personally I prefer to go further away in search of a comp star (speaking of naked eye observations only) than to use very different comp stars.Best wishes,Sebastian Otero.

knowing comparison stars brighness

I agree with Sebastian, than knowing the brighness of the star helps. Even better to know their color-index. Actually if I know that one of the comp stars has slightly redder color, I use it buch more carefully -- especially taking into account the higher color sensitivity of my eyes.

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