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 was wondering what parameters I need to know/measure to calculate the velocity dispersion of a galaxy, specifically an AGN. Also, I have spectra where there are blueshifted and redshifted ...