Finally, one of the great magical women scientists! Hesper Starkey (1881-1973) was one of the greatest female potioneers of the 20th century. She is best-known for her study of how the phases of the Moon influence the brewing of potions.

Hesper Starkey began her schooling at Hogwarts in 1892, at the usual age of 11. At the opening feast, she was promptly sorted into Ravenclaw, which heralded her intense interest about research. She quickly became known among the professors and peers as a serious questioner, and could be found most days reading in the library late into the night. She also proved very early on in her education that she had a knack for potions. It is rumored that she was even more of a brilliant brewer than her classmate, Albus Dumbledore.

After graduation, Starkey continued with her pursuit of research when she began combining her two loves - asking questions and potioneering. While in her sixth year at Hogwarts, Starkey had begun reading about the ways in which the phases of the Moon affected magical plants. This simple book about herbology led her to begin questioning if the phases of the Moon affected anything else - like the potions that were made from these plants. However, it wasn't until she had procured a job with the Ministry of Magic that she was able to proceed with her research.

It wasn't until Starkey was in her 40's that she published her first major finding - the effect of the Moon on fluxweed and its subsequent potency in the Polyjuice Potion. Starkey discovered which phase of the Moon fluxweed was picked during had a major impact on the potency and safety of the Polyjuice Potion it was brewed in. 

Before Starkey's research, there was no standardized method for picking fluxweed to be used in a Polyjuice Potion. As a result, that potion was even more tricky to brew in the mid 1900s than it is today. Fluxweed picked during a new moon would cause the Polyjuice Potion to be much less potent than expected, often resulting in shorter periods of transformation. Fluxweed picked during a waxing moon would result in a potion with strong potency, but also was more prone to accidents. It wasn't unusual for drinkers of the potion to suffer some adverse side effects, such as permanent change of eye color, hair color, or height. And, fluxweed picked during a waning moon could cause even more serious side effects - to the tune of sprouting extra limbs. 

Starkey discovered that fluxweed picked during the full moon yielded the safest - and most potent - batches of Polyjuice Potion. Her discovery greatly decreased the numbers of number of Polyjuice Potion-related accidents per year. 

Starkey's later research contributed to the methods of brewing Veritaserum - it takes an entire moon cycle to brew. She continued her research into the Moon's effects on brewing until she died at the age of 92.