is the birthday of Arda Alden Green, a biochemist born in 1899 who explained the secret of what makes fireflies glow.
Focusing first on medical research, Green did groundbreaking studies of hemoglobin's interaction with oxygen in the blood. She also isolated and described angiotensin (a hormone that regulates blood pressure), phosphorylase (a critical enzyme involved in conversion of carbohydrates to energy), and serotonin (a molecule involved in many processes, including pain, sleep, and psychological function).
Green turned to fireflies in 1953. She crystallized the enzyme luciferase and teased apart the reactions it catalyzes to generate the phosphorescent molecule responsible for the insects' glow. She died in 1958.
Source: Benjamin F. Shearer and Barbara S. Shearer, Notable Women in the Physical Sciences: A biographical dictionary (Greenwood Press, 1997).