Today I started Astrophysics with my second year classes so built the solar system in interactive physics (obviously). The point I try to make is how hard it is to work out that the planets are orbiting the sun by watching them from the Earth. The image is what you get if you plot the paths of three bodies orbiting the sun taking one of them as the reference point. My students thought the way art came out of the physics was quite cool. I'm not sure its art and I'm not going to ask Reidun the art teacher.

"Chris, you may think that but you know nothing about art".

Most of the Geogebra resources I have been preparing lately have been for my first year students. I am worried that my second years will feel left out so made them an HR diagram. Setting up the axis is very contrived (they are done manually) so I don't think its worth them making one themselves but heres the one I made. I tried to get the colour of the dot to change from red to blue through yellow as the temperature is varied but I failed.

Not content with failure I thought about it a bit more and worked out how to make the colour of the point change. Not quite realistic but in the right direction. Problem is no trace is left when it turns white.