https://en.wikipedia.org/wiki/Ejnar_Hertzsprung
Ejnar Hertzsprung - Wikipedia
ejnar hertzsprungwikipedia
https://www.astronomy.com/today-in-the-history-of-astronomy/oct-8-1873-the-birth-of-ejnar-hertzsprung/
Oct. 8, 1873: The birth of Ejnar Hertzsprung
Oct 8, 2025 - Today in the history of astronomy, a pioneer in star classification is born.
oct 8the birth1873ejnarhertzsprung