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PHD2 drift graph - some sort of colinearity?
Hi all, Bill here
I'm still pretty new to this, and there are lots of things I don't understand, but like all the other noobs, I'm ploughing through anyway.
Last night I set up my NEQ6 in the back yard, and only after I'd levelled it carefully did I find that a tree had grown slightly and was obscuring Sigma Oct. Bummer. Well, rather than move and re-level I thought I'd try drift alignment using the PHD2 tool.
It seemed to go OK, and I got reasonable tracking afterwards (well, reasonable for a tripod set into soft dirt), but one of the graphs I got during the operation interested me. From memory I was adjusting the altitude, looking west, but not terribly close to the horizon as there's a house in the way.
As you can see I hadn't quite nailed the adjustment yet, 'cos the red line is trending down, but that wasn't the bit that was weird. There's clearly some negative relationship between Dec and RA in the graph. I suspect that it's multicollinearity (that is, a third factor causing the two lines to move in an apparent relationship).
Does anyone know what might be the cause? It might be the fact that I was sighting high (prob 30 deg) over the west horizon, so not in the ideal spot, meaning that the star drift was diagonal rather than perpendicular to the axis - if you know what I mean?
(also, the graph is telling me I had a polar alignment error of 3.75. Is that arc minutes? While that wasn't the end of my drift alignment exercise, what is considered good for a portable setup?)
Thanks!
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