The big magnet

I'm working late again tonight, preparing a lecture for Friday morning. Tomorrow night I'm taking Little Boy to skiing practice, so I have to prepare the lecture one day in advance. It doesn't mean I've got better habits, starting early. It's just because I have to.

The subject this week (for the lecture, not the skiing practice) is magnetotellurics. It's a crazy word composed of two parts:
o Magnet; everyone knows what a magnet is.
o Tellus, which is the The Earth.
The Earth (Tellus) acts like a huge magnet. That's why such things as an old-fashioned compass works. The arrow points towards the magnetic north pole of The Earth. The magnetic north pole is different from the geographic North Pole. So if you're very close to the geographic North Pole, your compass would point to some place in Canada rather than towards north (you better use GPS in that case).

Furthermore (and this is where the fun starts), our dear Sun sends out so-called solar winds, continuously. A swarm of electric charges is raining over The Earth, and pushing the magnetic field out of equilibrium.

Just relax. It's not dangerous, and there's no way to stop it. This will go on until the sun stops burning (which will be really dangerous, but it's still some billion years into the future).

When the earth-magnet is disturbed like this (by the solar storms), The Earth sends back an echo which reveals it's inner secrets, not all the details, but more like a rough sketch. If we put down some sensors and measure the echo, we can compute an image of the earth and it's inner structure, many kilometers below the surface.

Cool isn't it? Do you wanna know how to do it? Then you have to come to my lecture on Friday morning. We're starting at 9am, after a cup of hot coffee >:)

(The picture above is an illustration of solar winds distrubing the magnetic field of The Earth. I took it from a report written by a former MSc student of mine. He (the student) probably stole it on the internet. I don't steal stuff; I just borrow it.)