Why does the Hertzsprung–Russell diagram's x-axis go from large temperatures to lower?

  • In my textbook, the H–R diagram’s y-axis is $\log(L/L_{\odot})$ and values are higher as we go higher on the scale, but the x-axis is $\log(T_\text{eff})$ and gets smaller as we proceed to the right.



    This confuses me. Why not let the x-axis go from lower values to higher values? This will also help visualising the “linear” relation between the luminosity and the temperature of a star in the main sequence.


  • James K

    James K Correct answer

    6 years ago

    Originally, what was plotted was luminosity against colour, and by colour I mean the wavelength of the peak intensity. Short wavelengths on the left, and long on the right, as you would expect.



    stars-planets-galaxies-qa.com



    Now since stars emit (nearly) black body radiation, there is a close relationship between colour and temperature. I suspect that the reason that the x axis isn't inverted when temperature is used is just inertia:- We have always plotted out H-Z diagrams like this and we will keep doing so.


    Originally what was plotted was absolute magnitude versus spectral type. If colour is on the x-axis then the diagram is known as a colour magnitude diagram.

    As indeed the picture in your answer illustrates.

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Content dated before 7/24/2021 11:53 AM