- Between Boötes and Leo lies a fan-shaped swarm of faint stars that was known to the Greeks but was not classed by them as a separate constellation. Eratosthenes referred to this swarm as the hair of Ariadne under his entry on the Northern Crown (Corona Borealis), but under Leo he said it was the hair of Queen Berenice of Egypt, which is how we identify it today.
- Hertzsprung–Russell diagram (Wikipedia)
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 and their stellar classifications or effective temperatures. The diagram was created independently in 1911 by Ejnar Hertzsprung and by Henry Norris Russell in 1913, and represented a major step towards an understanding of stellar evolution.