# The Hertzsprung–Russell diagram

#### Question P9.2.3

The Hertzsprung–Russell diagram classifies stars on a scatter plot: each star is represented as a point with an $x$-coordinate of effective temperature and a $y$-coordinate of luminosity, a measure of the star's radiated electromagnetic power. The compressed file hygdata_v3-abridged.csv.gz represents a version of the HYG-database, released under a Creative Commons Attribution-ShareAlike license} which provides data on 119614 stars.

Read in these data with pandas and plot a Hertzsprung--Russell diagram. The luminosity column is identified as 'lum' in the header and the star temperature can be calculated from its color index (also referred to as $(B-V)$ and identified as the column labeled 'ci') using the Ballesteros formula: $$T\;/\mathrm{K} = 4600\left( \frac{1}{0.92(B-V)+1.7} + \frac{1}{0.92(B-V)+0.62} \right).$$ Note that the luminosity is best visualized on a logarithmic scale and the temperature axis is usually plotted in reverse (decreasing temperature towards the right-hand side of the diagram).