Completing an astronomy word search today I came across the word HR Diagram and looked it up. Add this one to the knowledge bank. The Meaning: The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications or effective temperatures. - Wikipedia. Interesting we can measure temperature of stars billions of miles away.
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From @sourblunts