I just bought my first oscilloscope and have been tinkering with the measurement of different signals just to learn the ropes and familiarize myself with the scope.
One of the first things I noticed was the ambient 60Hz "noise" that is picked up when a probe is connected to the scope. It is obviously originating from the electrical lines in the building, and I can verify this by holding the probe in my hand and placing my other hand nearer or farther from an electrically powered object or cable - the amplitude of the noise increases or decreases respectively.
Then I probed the mains voltage to see how clean the incoming power is. Next, I viewed the aforementioned 'noise' signal on one channel and the mains power on the other channel.
What I saw was surprising and I don't understand the reason: The mains voltage shows a clean 60Hz sine wave. The 'noise' signal is a jagged sine wave, still obviously 60Hz but with a lot of static. However, the two signals are out of phase, by what appears to be approximately 90 degrees if my measurement is correct. I would have expected the phase of the mains power to match the phase of the noise. I was concerned my scope had some sort of delay between sampling the two channels, so I switched the inputs and still saw the exact same phase difference. Attached is a screen capture showing the two signals (red = mains, yellow = noise).
A little more research shows that transformers can cause phase shift between the input and output sides. (TI pdf) Is this what I'm observing? or is something else in play?
If I'm missing a basic point, please help me understand it or at least guide me in the right direction.