I did a mid-morning solar from a sprinkler head in my backyard to a TV antenna several houses away.
It's about 10' from the rear lot line and there are overhead 12KV power lines (and 220 volt secondary, telephone and two cable TV company lines) so I figured compass bearings would be way off.
I'm surprised, my compass reading on both my Transit and my staff compass are less than 1/2 degree off. An iron patio chair (I stood on to get my avatar photo) pulled the needle a degree and half though.
I established a point in the front hard which reads about a degree off. That could be influenced by an iron gas line and parked vehicles about 30 to 40' away. I thought the front yard point would be magnetically cleaner, but maybe not.
A lot depends on the orientation of the magnetic fields. Sometimes they really mess things up - sometimes they're in alignment so they don't have much effect.
AC fields don't have much effect on a compass since they are trying to vibrate it back and forth 60 times per second and make no net pull. I wouldn't worry about the current in the high voltage lines. They probably have steel in the wires for strength, though.
DC will cause a bias. I think the cable TV sends DC power down the cable to run distribution amplifiers. The current could return on just about any ground and not cancel the local field, so could have a net magnetic pull. I could be wrong and the power could be AC with rectifiers in each amplifier box.
I have found a lot of variation (BA HA HA HA!!!) in objects pulling the needle asunder. It appears to be erratic and not predictable. Sometimes I have observed overhead KV effecting it and sometimes not. I have observed some raised sanitary sewer manholes I was standing on pulling on the needle, while others don't.
One must excercise care and take several observations to see if their compass is being effected.
Intersting point about the AC vs DC, Bill.
Stephen
Polaris
I just found Polaris at 7:13pm which is 1:20 before Sunset at 8:33pm here.
I have had no problem finding it at sunset but this is the earliest I have been able to find it. It is very dim in the telescope.
I tried to put it under the intersection of the cross hairs which made the residuals of my two sets a little rough (10"). It's easier later because you can see it under the cross-hair.
If I would aim a little high so that Polaris is in the gap in the vertical cross hair then it should be no problem getting a good horizontal angle.