Thanks for Fritz Obermayer for the idea!

What is needed

What to Do

What is Happening

This is one of those experiments that, to be perfectly honest, we don't totally understand. We have some idea of what is going on, but our understanding is not complete. On the other hand, this is so cool that we decided that we had to share it with folks.

The picture on your computer monitor or your television set is drawn with an electron beam. So it is no surprise that the screen builds up a static electric charge. Most screens build up a static charge when you turn them on; this gradually goes away. Then, when you turn them off, you get another static charge - the opposite sign of charge this time. You will get a uniform charge over the surface of the screen. The dust particles on the screen will get charged up, and will be attracted to your finger.

When the dust particles jump to your finger, they do so in the star pattern that you have seen. We are not quite sure why this happens. If you watch, you can see the dust particles migrating toward your finger - and away from each other. They also migrate toward clear regions of the screen. It seems like the dust particles, which are all charged the same way, will repel each other and attract your finger. And once you have cleared some dust particles from the screen, the remaining particles will be attracted to this region - but once they start moving, they might keep moving all the way to your finger, leaving a trail of clear screen.

Other Things to Try

Maybe you will be the one to figure out just what is happening. This might be a nice topic for a science fair project. Will different kinds of points (like a pin, or a pencil point) make different patterns? Will different monitors make different patterns? Does humidity matter? (We are in dry Colorado, and static stuff tends to work really well here.) If you find anything out, please let us know.