Why does spectral class and U-V colour correlate slightly differently for main sequence, giant and supergiant stars?
In this diagram the $x$-axis is spectral type for stars and the $y$-axis is B-V colour. Taking Series 1 as the Main Sequence, Series 2 as Giants and Series 3 as Super-giants. Why the spectral class ...
I have asked this on Physics Stack Exchange but Astronomy is probably more appropriate. I have been given the task of synthesising an elliptical galaxy, a starburst galaxy and a spiral galaxy ...