Neat freebie for the science freaks amongst us (astronomy)
OK, I just got the July copy of Scientific American yesterday. OK, it is actually going to cost $6 to get to it but in the middle is a free foldout poster of the Hertzsprung-Russell diagram.
Note for those not really into this, it is a visual graph of the stars that shows them on the X axis by surface temperature (color) and on the Y axis by absolute luminosity (brightness if each star was a standard distance from us).
It turns out that when you sort stars out that way, you can learn quite a bit about them. For example, all the stars that have not yet gone into what amounts to old age fall on a generally diagonal line from top right to bottom left. The position along that main sequence line is directly related to the mass and chemical composition of each star. As stars get old, the move toward the top right and then when the finally die, they fall to the bottom left.